Some notes about the beta:
Level 13 is the highest you can get in it, and the story/game ends once you beat a certain boss that I won't spoil, takes about 2 hours or so to go from start to finish.
You finish the beta at lvl 8-9, but can join public games (with a max party of 4 people) at different "checkpoints" in the chapter, requiring certain levels to join up (as you are at a certain point in the story). So, tonight I ran 3 of the last boss dungeons with 4 people each time, gathering blue and yellow items (not sure what they are called yet) to disenchant to level up my blacksmith guy (level 12 right now).
So, yeah, it plays a lot like D2. You start a game on normal difficulty (the only one available in beta), finish the beta, then the only other things you can do is:
1. Start a new character
2. Start a new game/join a public game with your current character to continue getting more xp/items to use for blacksmithing/fun, until level 13 when you max out.
Barbarian is the most powerful class in the game right now, at least from what I can tell. You can destory rooms of guys faster than the other classes (haven't played demon hunter so don't know about that one), and their skills really build around massive AoE damage with Cleave, Stomps, and your Leap ability, and because 95% of the time you are fighting 5+ enemies at once, it deals SO much raw damage. This might change at end-game or on release, but right now Barb simply destroys more than the other classes.
Rest of the classes are solid and fun, but I hope the Barb is nerfed just a little bit before release so that there aren't 50% of the player base playing a Barb while the other 50% is a mix of the other 4 classes.
Anywho, great game, can't wait for release.