This is my bias: Diablo 2 is my all-time favorite game. I despise Blizzard for a lot of things they do (especially business-wise), but the Blizzard North people rocked and made an amazing game, and I'm willing to look past the company IF they make a fun game. I've been waiting for D3 ever since, as it was obvious they'd have a sequel. BUT.... everything I've seen, read, watched, etc. up until this point has made D3 a major disappointment.
Characters I've "finished" the beta with so far (and thus the only ones I have experience with yet):
Whew, that's a lot of typing. I'm sure there is plenty more I'm forgetting since I'm just writing this up off the top of my head, but those are my impressions so far. I know there seems to be a lot of cons, but I just wanted to be a bit more in depth with them. Sadly I've spent more time playing Saints Row The Third than the Diablo 3 beta, and if you know me, you realize how insane that is... it is rather telling in regards to how I feel about D3 thought.
Overall I'd say that I think the game will be fun (I already have it preordered and WILL be playing when it launches). It will just be a huge disappointment for anyone expecting a true Diablo 2 sequel. It's dumbed down, boring looking (by comparison), and just not at all what the Diablo franchise should be.
BUT, if you don't care if it's Diablo or not, you'll enjoy it. As a standalone game it IS quite fun, but I definitely don't see myself being as fanatical about it unless the other acts are just mind blowing.