Best. Game. Ever.
The combat is so fast paced, the quests are fun (and for every quest you complete, they give you a new one), the interface is great, and it's so awesome that you could get to 60 without ever XP grinding on mobs.
The interface is the best of any game I have ever seen! The spells on your hotbar gray out when your target is not in range.
Every class is fun (admittedly, I've only tried 5 so far), every skill is useful (also admittedly, I've only played to level 10-12 with those classes), and did I mention the awesome quest system?
I've only been playing since Tuesday (where I forgot to eat dinner), but goodness...I haven't been this giddy about a game since the leap from EverQuest 1 Beta to DAOC.
Blizzard has certainly redeemed itself from that Diablo II fiasco...

Yeah, I totally agree.
I've been beta testing (closed beta) for quite a while - thanks to Sungsoo aka techman (old CHV days) - and leved up to 24 as a female human mage. Man.. surviving as a human mage.. is not even funny. But after lev'ing up to around lev 18, things started to get fun.
I can't play anymore because: 1. too much work, 2. I'm playing Winning Eleven 8, 3. too much work.