I have been in the Beta for a couple of weeks now, between Skyrim and MW3 I haven't had a load of time with it but impressions so far (after the latest patch):
1. It needs optimising. I can run Skyrim on high at stable fps but D3 lags a little too often, also the netcode is still a bit shakey, my gf was web browsing last night and my bar went to yellow and it was lagging far too much, I could play WoW without a hitch while she streamed from iPlayer before now. I assume the servers for the beta are US based maybe.
2. The demon Hunter still needs work, even with the new system they just feel gimped at low levels compared to the rest. Hungering Arrow needs to do more damage or impale spend less hatred imho.
3. Mele Wizards are great.
4. The barb will be the most fun to play imho, sending zombies flying never gets old.
All in all though, it feels like Diablo, which is awesome.