By and large Diablo III is exactly what I'd have expected from the next game in the series. An interesting but not terribly surprising story. Copious numbers of monsters to kill. An insane amount of random loot to sift through. Escalating difficulties. An annoying sand level. Clicking, clicking, clicking.
There's one major deviation from my expectations and it makes me a little sad. That difference is a very achievable level cap. I can remember Diablo II having a ludicrously high level cap. There was a brutal experience curve such that there were very few monsters you could fight that were even worth experience once you got high enough. In fact, if the internet memory serves me correctly there was exactly one monster worth experience. Diablo himself. The first character to max level had a team of people helping out. They'd kill every monster in the zone, spawn Diablo, and knock him very low. Then Gerbarb would tag in and get the killing blow in an 8-player game. They kept this up in parallel making sure there was always a Diablo to go kill. He didn't waste any time killing random non-Diablo dorks. Apparently they were able to kill 3 Diablos every 10 minutes! (And also had extra characters running around the games looking for experience shrines!)
It took them almost 44 days to get to max level and it took a team of dozens of people to get it done. It took me a little over four days to max out in Diablo III. I played a fair bit but some of that time was on an alt. I didn't put any special effort in. I didn't have a team playing my character. I didn't have people setting up games to farm. In fact I finished off by replaying Act I!
Now there are still things to do. Gear to twink out. Inferno difficulty to beat. Other classes to play. Achievements to earn. I'm not saying I'm done with the game. But being able to hit the level cap so easily just doesn't feel like Diablo. (Perhaps the biggest difference is the lack of a death penalty. I could never have maxxed out in Diablo II because I don't play cautiously enough!)
I wish the game had a stupidly high level cap. There's no need to have gear needing that high of a level. There's no need to have the final levels be big power increases. But there should be more levels differentiating people!