I don't really have any problems with the d20 system. I found that most skills and classes revolve around combat which sometimes make me wonder why the rest of the skills are there. Mind you, I'm sure any good DM could make those skills worth their while.
Recently, in Neverwinter Nights, I've started playing as monk. The only thing I'm finding is that I can only seem to make one sort of character. I feel like it would be a waste not to use the pre-determined feats.
Are you using d20 or d20 Modern?