Played through as a Wizard and Witch Doctor. I have to say I was quite underwhelmed, this game is Call of Duty with swords and magic.
It's polished and reasonably fun but there is very little depth. I'll be waiting until the game has matured a bit to see if the endgame is any good, because I can't see it being very challenging based on what I've played so far.
To be fair it's impossible to judge from what we've seen, you'd think the same about Diablo 2 if they gave you the first hour of that.
It's meant to get really hard.
This!
I've played Diablo since the first one came out in 1997, finished it with every class then did the same with Diablo II and all the expansions straight on release.
I have to say it reminds a lot of Diablo 1 when you get into dungeon which is nice.
The normal difficulty was never hard and should be finished easily by anyone who can use keyboard without looking at it every 5s to see what he's pressing.
I've finished both D1 and D2 on all the difficulties with any class and I've got to say that the game should be getting A LOT harder on the 2nd and 3rd difficulty level. Also it will get a lot more intense in higher acts.
Remember D2? You could nearly finish the whole first act there all the way to Andariel ruins without wearing any items and adding any points to skills.
What I was more concerned is that early betas over year ago showed the game as a lot slower - they seem to have improved that a lot, everything is super fluid, fast and smooth which is awesome : ).