I also played in the open beta and lets just say, saturday I got on one, lagged for awile, and then they shut the servers down and then Error37'nd everytime till much later on when "looking at the D3 forums" people were saying they were getting in.
I had a chance to play every character all the way through even got a monk to full level (13). I started with D2 in college in 2002 and found skill trees to be sometimes confusing, but reading a guide helps (I was still really new to the whole online game world). The lack of them was a little depressing, only because particular character classes had a move that was way better on second tier, and going back to the origional with a rune in it, didn't seem like an option when killing mobs. So it basically felt like "oooo a lvl what did i get.........oh...nvm" but as in most MMO styled games (even D2) you have to sink a point to unlock the next tier which i understand.
The only issue that would/will keep me from aquiring the game is the constent need for an internet connection, even just to play single player. Just the fact that, if they take the servers down for mantanance, you can't even play the single player campain while you wait. This thought in its self is mind bottling, I can understand the need to take out chances of Piracy but that just seems like to much that i would pay $60 for ownership of a digital copy of a game provided by a company, that said company can inhibit that person, simply by doing something to the server is just bad markiting (i also see "the cloud" like this as well)
Also I would like to see an ability to, after making a game open to the public, being able to close it to the public again w/o having to reload the character. Although i can see how this would be used as a means of "screwing" other players (possabily) out of "fat loots"