Read for an honest review of the game without the fan-boy or blizzard hater bias.
The biggest downside of Diablo 3 is probably that it requires an always on-line internet connection to play, even during single player. Lag will often cause the game to freeze up or your character to jump back to previously traversed spots. If you ever drop your internet connection, you are booted back to the main menu and are forced to reconnect. This results in you respawning at your last check point with all the previously killed enemies resurrected. It would have been better if Blizzard rather implemented this control in much the same way as they did Starcraft 2, whereby you need an internet connection to login, earn achievements, and of course play multiplayer, but not necessarily to play single player.
If you loved the previous RPG elements of Diablo 2 then this game represent a significant step backwards in a number of ways. Skill points have been done away with and instead you are awarded skills and/or runes (upgardes to skills) when you level up. The assigning of stat points is also gone and the game automatically assigns additional stat points when you level up. This in turns means that stat requirements for weapons and armour have now been done away with and instead replaced by level requirements.
Compared to other Action-RPGs the gameplay has also been dumbed down a lot. As character customisation has all but been done away with there is really not much strategy involved beyond moving your character around, select the right skill, and clicking relentlessly to attack your enemies. The gameplay is so simple that if it wasn't for the games dark storyline it could have probably gotten away with an 8+ age requirement.
Fans of the series will find that the story is the biggest and most attractive element of the game, and will enjoy seeing how the war between the high heavens and burning hells unfolds and your part in it. But you aren't likely to feel emotionally invested in any of it. The story is extremely linier and it would have been nice to be able to steer the narrative a little based on choices that you make during conversations, even if these choices had no effect on the over all story.
The environments and effects are breath-taking and extremly polished. The new art style which initial caused such an outcry on the web was a good choice and Blizzard certainly has upped the bar in this regard. But, unfortunately beyond the environment and the effects that is about it. The camera angle cannot be adjusted and you can never get in really close to your character to admire any of the details in your newly acquired armour.
Followers have also received a small upgrade. You now have the choice to pick between 3 different companions which are standalone characters in the game each with their own back story and personality. When they are not assisting you in battle they patiently wait at the camp site, and at times talk between themselves which can add a little comedic relief to the game. Each of these companions also has their own set of skills and gear, albeit very watered down, which can be customised.
Two crafting systems are also a nice addition to the game, a blacksmith for weapons and armour, and jeweller for adding gems and sockets to equipment. Each of these crafters can also be upgraded which allows access to better gear. A particular nice feature is that these upgrades are extended across all character on your account so when you start a new character you will already have access to all the previously unlocked upgrades. Crafting is done by the way of breaking down magical and unique gear into two crafting components which are then used to create new items. Also, items are not "soulbound" to your characters so when you are done with them you can pass them onto someone else or sell then at the auction house.
Multiplayer doesn't really add much to game beyond a social aspect, but at the same time Blizzard has been very clever not to have it take anything away either. Unlike most other Action-RPG multiplayers when you join a friend on-line you essential become part of their game and any progress gained in their game doesn't affect the progress in your game. In Diablo 3 their progress becomes your progress, and when you break ties you continue playing from where the multiplayer game left off. The only downside being that if you join someone who is further along than you, you end up missing chunks of the story, with the inverse being that you might end up having to replay certain sections. However Blizzard has cleverly accounted for this by allowing you to select section of the story from the main menu and either jump backwards or forward to that section of the story. Two key features missing from multiplayer is PVP and voice chat. But considering the lack of any character customisation PVP wouldn't really add much to the game anyway, and the lack of voice chat is an easy work around with the likes of Mumble and other similar voice chat programs.
Fans of the World of Warcraft series will the find the Diablo 3 auction house very familiar, but with a newly added feature which allows you to buy and sell equipment and gold for real world money, a first for the gaming industry. However this feature was not avaiable at launch so if very hard to comment on just how effective it will be or how much enjoyment it will add to the game.
In summary Diablo 3 definitely has good entertainment value and is worth buying and playing. But beyond the real world money auction house and beautiful environments don't expect to see anything innovative and/or new to the genre or industry. Maybe it is just the hype but it is not what I expected from a developer that set the bar so high for the Action-RPG genre over a decade ago.