A friend I play with does the monk, and he's a blast to play with. He's got some nice attacks, gets a pet, and can do some healing buffs. Having Dexterity as a main stat seems to do some good things for the class, since they get it boosting damage, armour, dodge bonus, and what have you.
I've only played the barbarian, and I think it's an okay class. I really think it suffers a lot from not having the full keyboard for skills; I'd like to leap into the fray, use a couple shouts, then pop some abilities, and be able to have the ranged abilities at the end there for the times I need them to pick off runners or annoying enemies that like to flit around and not directly engage (act 2 sand wasps, I'm looking at you).
The one thing I guess that is kind of bugging me is that two-handed weapons seem pretty shafted. There just never seems to be any I come across that makes forgoing an off-hand item worthwhile - it's giving up up to five extra magic effects. The effects on two-handed weapons don't seem stronger than one-handed ones, and the DPS is only marginally higher at baseline.