I played Diablo 2 and LOD, and I must say that I think they did a pretty good job with this game. I do admit that melee classes (monk and barb) are extremely gimped when it comes to late-hell and inferno. How can they fix that? I haven't the foggiest idea, but I think that something needs to be done to make them more viable classes. I've also heard a lot of people complain about the fact that there's only "one viable spec" to finish Inferno. As that may be SOMEWHAT true, I think people lose their perspective. The reason that diablo 2 had more "viable specs" is because Hell mode was an absolute joke. Anyone could solo it by the time you hit 85-90 with ease if you had any kind of OK gear.
The crafting system, I agree, is kind of stupid. The only reason I'm trying to level them both to 10 is because I want the achievements. You can spend 60k trying to get 1 good item for a level 25, or you can go spend 10k on the auction house and get 2-3 good items that are better than what you would have made yourself. it could be different in Inferno for the level 60 gear with all of the recipes and such you can find, but I haven't played much of inferno so I can't say yay or nay on that.
I think the gameplay (after Normal and most of nightmare) is wonderful on this game compared to Diablo 2. D2 was easy, D3 is hard. The scaling they did through the difficulties is immaculate where it gets exponentially harder as you go up them (Especially Hell -> Inferno. if you haven't played in inferno yet, you're in for a big surprise).
Overall, I give the game an A. Replayability is good, graphics are good, skills are good, crafting is meh, lore is awesome (I think

, and I enjoy the friends list system MUCH better than Diablo 2.