I bought D3 a few days ago. I played it most of the day today. My Monk is now level 24. I wasnt very impressed with the game at first, but now that im fighting massive packs of mobs, its much funner. The boss fights are more WoW-style, as opposed to D2 style where you just bash them.
The skill system is different. It lacks character customization, but i can switch skills for different fights if i choose to, allowing me to solo more content than in D2.
Honestly i would rather have had another Diablo 2 expansion, and have D2 cleaned up to how it was on patch .09. Im not impressed with the 3D graphics. I like D2 style. Add a few more Diablo 2 characters, more acts and difficulties, and im a happy player. D2 remains my favorite game of all time.
But i do recommend this game.