Horrible DRM, many features removed, no RP, no LAN, no offline and hacked relentlessly by the second week.
Always online DRM require you to be at Blizzards mercy, play with their buggy servers, with severe lag.
Diablo 3 has no LAN, No open net because Blizzard is scared hackers will use the files to destroy their new cash cow auction house.
Diablo 3 has No skill trees, No skill points, copy & paste characters with only gear differences making the only difference between your character and the next the gear you got at the cash cow auction house.
Diablo 3 is being hacked relentlessly by the second week. With over 28,000 threads (not posts THREADS!) worth of hacked players on Blizzards own forums. Blizzard is outright denying all of it, It's so bad two games journalist have been hacked one of them a eurogamer reviewer who gave the game a score it didn't deserve.
Blizzards Greed driven answer to this was to make a buck out of the hackings and aren't interested in helping people, only selling their broken and bypassed authenticators.
Meanwhile Blizzard just keeps on denying the problems with their game. While trying to spoon feed their customers garbage.
DO NOT BUY THIS GAME!!!
Go over have have a look at Torchlight 2 by the actual Devs that made Diablo 2. They're giving the fans everything that they ever dreamed of in a looting and hack n slash RPG