I never played much of D2, but the consensus among my friends that did seems to be that Diablo 3 simply isn't rewarding enough. Legendaries and set pieces drop too infrequently and the rare (yellow) items are almost always useless for your character, so the auction house becomes the source of your upgrades instead of the monsters dropping loot, which really kills the drive to keep farming. I felt this pretty quickly too and I'm not motivated to play anymore. That being said, I definitely got $60 worth of entertainment out of the game, and if the expansion can solve the problems from the main game, I'll buy it on day one. The gameplay itself is a lot of fun, they just need to stretch out the item hunt some more, add some more interesting affixes, and maybe balance some of the abilities so that they can all be more useful. They're very close to another addicting game.