Hiro is freakin' awesome, Claire is fun to watch and most of the characters are interesting if not exactly likeable people. (I've not seen the most recent episode, so don't spoil anything.)
The only character I really dislike is Nikki, or more specifically, I dislike how helpless they've made her against her alter ego. This is something I see more as a flaw in the writing than any fault of Ali Larter, though.