Enormous disappointment, but not evident at first.
There is not nearly enough content to support their gaming model, and what is there is very repetitive and tedious. You have to go on quests several times to gain levels, and you get less exp each time you do. Wheeee. Even considering this, you can easily hit the game's max level of ten in about two months.
Combat is a twitchy mess. It's still the old 'autoattack and wait' grind, but you now have to chase the mobs around in circles. I'm not sure how they think this is more fun, but it seems some like it. Most do not. Forget about trying to use special feats or skills. No time.
There's no first-person view at all. Some prefer this, but it totally kills immersion for me. I just couldn't get used to looking over my own character's shoulder. There should at least have been an option to choose between views.
All dungeons are instanced, which some prefer. I don't. I prefer a mix. For those who play EQ, this is like doing nothing but LDoN's forever...but for less exp and loot each time you do it.
There is only one city, not a huge world to explore. All dungeons are quickly accessed from said city. Some folks like this instant access to the action, but for me the whole game seems claustrophobic and unfinished.
There is no bazaar, there are no tradeskills, there is no zonewide chat, there is no PvP, and several races and classes from DnD are missing, though they will probably be added in expansions later. Take these facts as you will.
Dungeons are rushed through. There is no real strategy or communication in the group. Everyone just bullrushes through dungeons to finish as quickly as possible. This leads to serious problems when some folks don't know the particular dungeon. When finished, everyone turns around and does it again. Other MMOs have 'the grind'. DDO has 'the rush'.
The interface is bulky and clunky. The inventory window is difficult to use and small.
The game is set in Eberron, which is almost universally despised by DnD players. Sorry, but I'm just not impressed with a DnD world that has super-powered androids as a playable race and driders with scorpion bodies instead of spider. There were already too many, better-written and developed worlds to choose from, from Greyhawk to Forgotten Realms, to Dragonlance, to Ravenloft. Why add a new one?
A few folks will like this game I'm sure, but as a long-time player of both MMO's and DnD, I am not at all impressed. Feel free to try the game, but if you play for more than a month, I'm afraid you'll wind up agreeing with me. Skip this one and wait for Vanguard: Saga of Heroes or Conan: Age of Hyboria.