If you enjoy fast paced, responsive action, don't mind the Eberron setting and the dated graphics, you'll enjoy DDO.
Sounds pretty standart, doesn't it? Well, it isn't. For starters, character customization is really deep. It's so deep, in fact, that unless you have a good idea of what you're doing the first couple of characters you create are going to be throwaway toons. You have a metric ton of parameters to customize: ability scores (like strength, constitution, intelligence, etc), skill points (jump, hide, swim, intimidate and many more), feats (like the ability to use exotic weapons, have a better chance of dodging attacks or resisting spells, or casting spells that last twice as long), and, if your chosen class allows it, spells. Then, as you gain experience points (or xp), you'll be gaining enhancement points which you can spend to, you guessed it, customize your character even further.
This may not sound very complex, but you should know that many of the most handy feats have some prerequisites you have to meet typically with your base ability scores, like extra attacks if wielding two handed weapons, or more powerful blows that strike all enemies within range if using two handed weapons, or the ability to trade accuracy for either better defence or more powerful attacks. In turn, many of these feats are themselves prerrequisites for many enhancement lines, and both feats and enhancements are required to unlock yet another layer of character customization: prestige enhancement lines, many of them being so powerful that it is really rare to see a character of a class like barbarian that doesn't get his only available prestige line (frenzied berserked). It's that good. And if all this wasn't complex enough, as you gain levels you can mix different classes and prestige lines as long as you meet the prereqs for all of them.
To help you create your first toons DDO lets you choose between some premade paths. Bad news is, many of them are terrible. To be more specific, I've been questing in a group with a kid that had a melee combatant (a monk) who had less endurance (measured in health points or hp) than the caster in the same group. When I asked this kid how had he distributed his ability scores, he said he had just chosen one of the available premade paths for monks. His game experience really suffered from poor path design as other players in the group blacklisted this boy because he couldn't help but die a lot.
Fortunately, Turbine seems to be aware of this issue and is creating some official beginner character guides you can find at DDO official forums (forums.ddo.com) which are really useful for newcomers. There are also templates for new players, which are really accesible, which you can find at the ddo wiki.
GAMEPLAY AND QUESTING
Once you're done making your first choices you start your adventures in an island, as a survivor of a ship wreck. This island serves as a tutorial, and is (IMHO) really well carried out. It lets the player get familiar with many crucial concepts such as avoiding traps, basic movement, advanced movement like climbing and swimming, locating hidden objects and doors, combat, and more. Once the basic tutorial is done (which you have to play solo) you arrive to a village in that island which serves as a more advanced tutorial, but this time you can begin joining (or forming your own) parties of players. DDO features its own guild system too. You can join a -or create your own- guild to chat or party with a semi-static group of friends, much like in any MMO.
DDO is an instanced MMO. This means that there are some areas that serve as hubs for players to hang around, trade, socialize, or do other tasks like selling and repairing gear. Whenever you enter an adventure, though, the game creates an unique instance for your group. There are three types of quests, depending of the size of the group allowed into them: solo quests (which are very few and far between; three or four at the very beginning of the game and one at endgame), regular quests (accepting groups of up to six players), and raids, which are special, more complex quests that often require some prerequisites to be able to participate (commonly referred to as flagging) where up to 12 players can join forces.
Let's make this clear: questing in DDO generally is a blast. Combat takes place in real time and it's very dinamic, even to the point of requiring twich reflexes. The second you press your left mouse button your toon will be performing a melee attack or shooting an arrow. You can press jump a split second before a caster throws a lightning bolt at you and, if you time it right, you will dodge his attack. If it sounds good, it is because it's that good. DDO also sports some nice sneak mechanics
(and sneaking can be a very powerful strategy) and excellent (if totally overpowered) magic combat. And make no mistake: magic users can do much more than throw fireballs or buff the party. Mages can become invisible, or incorporeal, teleport to different locations, and more. Not all quests allow for the same degree of gameplay flexibility, but many of them really capture the feeling of pen and paper DnD.
THE SETTING
Quests are very varied, and there's an abundance of them at all level ranges, though early levels show more variety than higher levels. The Eberron setting might not be for everyone: Eberron is a high magic, advanced tech fantasy setting with flying ships, sentient robot-like machines called warforged you can choose as a playable race, and even robotic dogs certain classes can have as pets. But even if steampunk is not your cup of tea, there are enough old-fashioned classical sword and sorcery quests to satisfy everyone.
GAME MECHANICS
As you quest, you battle orcs, kobolds, lizardmen, slimes, giants, ogres, zombies and demons, gaining experience and, of course, loot. There are three different kinds of items: randomly generated loot, named loot, and crafted loot. Between the named loot, raid loot (as opposed to regular quests loot) is the most powerful loot one can get. To prevent you from gaining raid loot too fast DDO puts your toon on timer each time you complete a raid, so you can't run it again in roughly two days and a half. There's one exception to this rule: Tempest Spine raid, which incidentally happens to be the only free to play raid -more on free to play later.
While the early levels and questing will most likely be an absolutely blast, from mid levels onward things can change drastically. Early on, you can succeed with nearly any build (a build is the pseudo-technical name given to the combination of race, class, ability scores, feats and gear setup you create for your character). But when you go past mid levels, there's a sudden ramp up in difficulty that will most definitely cull the unprepared, and rather harshly. It doesn't help that the game is based on core 1d20 mechanics and a lot of hidden numbers that certain foreknowledge of what to expect to have a small chance of success once you hit places like Gianthold or the Vale of Twilight (both mid-to-end adventure settings).
So that you get an exact idea of what to expect, let's go over a core concept that is crucial to the game. DnD is based on dice rolls. When you attack, the game makes a roll which is what determines if you hit or miss. That roll is always a 1d20 roll. You add your strength, class attack bonus ,weapon bonus, etc. to your attack roll, and to connect with your opponent you must beat his defense score, which is in turn the sum of things like his shield, armor, reflexes, magic barriers and all. Bad news is, modifiers can go up to 60 easily, but the dice roll is always 1d20. Imagine you have, say, an armor that gives you a defence score of 15, add a shield on top of that for 10 more, then work on your reflexes to get 5 more, and use a magical deflection item that boosts your defensive score 5 extra points, That's 35 defense. If your opponent has an attack modifier of 40, his attack rolls will always be between the 41-60 range, meaning your defenses are going to be worthless. You might as well run around naked because all your defenses amount to exactly nothing. Zero. Nada. Zip.
What is worse: one would think getting a better shield that gives 2 extra points of defense and gaining a feat that adds 1 to your reflexes would help your toon's survivalability. It won't. If you had 35 defense, and added 2 from shield and 1 from your reflexes, you would have 38 defense points. Since the listed opponent has an attack bonus of 40, his lowest attack roll would be a 41, so your theoretical improvements to your defense are utterly meaningless. The feat you spent on your reflexes, far from being of any use, is just a little step towards making your toon a failure.
Seasoned players either build their toons for maximum defense score (named armor class or AC in the game), or forget about it altogether right before hitting the aforementioned game areas (Gianthold or Vale). New players oblivious to this knowledge are bound to build washed down toons that will be seriously underwhelming at endgame. Even if you decide to focus on your defense: a new player is very likely to needlessly sacrifice a lot of offensive power and still fall short of the milestone numbers needed for endgame tanking. Defense builds are some of the most gear intensive builds of all DDO.
Tactics must also evolve. Before hitting the Vale of Twilight area, most enemies you faced would either use spells or ranged weapons, or go melee and attack you. But they needed to get in line of sight or be close to you and facing your toon to harm you. Endgame introduces a new class of enemies, called devils, that teleport right behind you and use cleave attacks, attacks that hit in a really wide arc -about 270 degrees. There's no running away from them, there's little sneak from behind. Characters who didn't build for maximum defense need to shift gears and settle for as many hit points as possible, and begin relying on magic that gives your enemies a flat chance of missing an attack. Magics such as the displacement spell, which makes your toon seem to be in a different place where he actually is, giving your enemies a 50% chance of missing any attack they attempt.
If all this sounds like algebra to you, welcome to the so very often handslapped mass of newcomers to DDO. These are the difficulties new players must overcome. Good news is, if you do overcome these shortcomings, you're in for a treat. DDO features some excellent quest design, great settings (both classical and steampunk), and astounding variety. And best of all, you can play some parts of it for free.
DEATH
Death of your toon in this game means a couple of things: your gear suffers some temporary damage, your group (and all players in it) no longer qualify for a 10% no-deaths-in-quest xp bonus, and you can't do a thing until you are resurrected, either by using spells or by taking your soulstone to any of the strategically placed resurrection shrines. Some quests have many of them, some don't have any. When all players in a given instance have died, you have two choices: either one or more players release their souls from their dead bodies to be resurrected outside the quest, then reenter quest to resurrect their falling companions (incurring in another xp penalty) and continue the quest from where they were when they died, or the group can disband then regroup to reset the instance they were in and restart the quest from scratch. Veterans often prefer this last approach to avoid the xp penalties.
FREE TO PLAY
You can play DDO for as long as you want without spending a dime, ever, And you won't be punished for it. A paying customer that rolls a toon that shares your same race and class and stat allocation gets no advantage for being a paying customer when he runs the same content you do. What he gets is way more content available, which in turn means more loot, and more rare (or named) loot. Especially raid loot. But even as a pure free to play individual you won't be totally left out. As you complete quests you earn the favor of different factions in the game, measured in favor points. So you rescued the lost girl from House Jorasco? House Jorasco awards you with 6 favor points. So you retrieved the stolen goods for the merchant's lobby, the Coin Lords? You just earnt 2 Coin Lords favor. When you hit certain favor milestones (such as 100 favor) you are awarded Turbine Points, the virtual currency which you can use to purchase things like extra adventure packs (Vale of Twilight being the most popular -and recommended- purchase).
There are three payment plans for DDO players: free to play (no purchase needed, ever), premium (you can buy virtual currency using real life cash then purchase whatever parts of the game you prefer), and VIP, which grants you unlimited access to all game zones and also some extra races and classes (but not all of them). Some of these extra races and classes can be unlocked via favor.
Turbine has, up to this point, made a decent job of not turning DDO into pay-to-win. Some recent additions to the DDO store are being the subject of heavy debate between the player base, but most would agree that spending cash on DDO won't make you stupidly overpowered. Controversial as some of these new items on sale might be, there are other free-to-play innovations that level the ground. For example, a recently added prestige enhancement line for wizards, the pale master, allows free-to-play races like humans to self-heal via magic spells or abilities, a rare feat formerly restricted to a pay-to-play steampunk-like race called the warforged. Warforged casters were frequently referred to as "DDO easy button". This is no longer true.
Free to play or not, once you hit the level cap (currently at level 20) you have only two things to do: strive to get better gear, or reincarnate into a more powerful version of your former self (or a different gimp altogether). Reincarnation is a relatively new mechanic that allows your toon to restart as a level 1 character, while gaining some perks from his past life. Those who were fighters in a past life will have a bonus to their attack rolls, whereas those who were wizards will cast slightly more powerful spells.
CRAFTING
Then there's the gear. And crafting. Some (or many) of the best items of the game must be crafted: be it the so-called greensteel items from the vale of twilight, or the epic Sword of Shadow. Thing with crafting is, it's a grind and a mess.
Crafting in DDO has so many forms, it's impossible to cover here in depth. Some players swear by it, some ignore it altogether except for the most common of its forms, the Vale of Twilight greensteel crafting system. There are many different crafting systems, most of them having nothing in common from the others. From the eldritch rituals that are based on collectables (items you can gather as you travel and quest, like mushrooms, pages from books, religious icons, strange larvae), to the raid loot-based greensteel system, to the epic item crafting lottery. Some just add a little perk to existing items, others create brand new objects of amazing power, others turn an old, outlevelled item into the ultimate weapon. But all most of them are different, and nearly all of them take a lot of space in your inventory as you gather dozens and dozens of collectables, components, or materials.
TECHNICAL REVIEW
Graphics in DDO feel outdated, not surprising given the game's launch date. That said, art design in many places is outstanding. While the DDO client is DX-11 enabled, textures can look bland, and spell effects more often than not don't look that impressive, though nearly all of them have an adequate graphic representation: blur makes your toon look blurry, fire shield shows your toon engulfed in flames, barkskin will give your toon's model a wooden texture, etc.
Sound is a hit or miss. Dungeons are narrated by different Dungeon Masters (Delera's Tomb quest chain is voiced by Gary Gygax, and Ruins of Threnal by Dave Arneson) to different degrees of success. Some sound effects are really convincent, others not so much.
The game suffers from some bugs. Most infamous one is the crash to desktop you are bound to experience when zoning in to a quest after having switched between toons and/or travelled between many different locations due to what seems to be some sort of memory leak. Also, having certain spell effects going off in screen at once can cause frame rate issues even in the latest systems, which is weird for a game that doesn't look that good by today's standards and that can be run in machines that have one fraction of a modern PC computing and graphics power.
CONCLUSION
DDO is a unique MMORPGs with an extreme variety of character customization options, a very characteristic setting -Eberron-, and outstanding gameplay and quest design. The game experience though is marred by obscure mechanics that lead to a very steep learning curve, technical glitches and outdated graphics. If you enjoy fast paced, responsive action, don't mind the setting (there are enough dungeon crawlers with little to no Eberron references) and can overlook those issues you are in for a treat. Just do your homework before you venture into the most demanding parts of Eberron.