Monks

[Xenogears]

1) MAD - Multiple Attribute Dependency, in case ya don't know. Monks have to have 3 to 4 stats be really high (Str, Dex, Con, Wis) to be any good. That's tough to do.
2) Flurry of Blows vs. all the other monk stuff - Monks have a bunch of mobility oriented powers and available bonus feats. The problem is that FoB requires a full attack action to use, so you can't use it in any round that you move.
3) Frontline melee without 3/4 BAB, low to decent AC, and low, low damage. Nuff said.
4) Useless abilities like tongue of the sun and moon, Quivering Palm (once a WEEK? Really?), etc.
5) Anything that makes a monk useful at high levels also makes a commoner useful.

Okay I get the first two. The third one. Well I never thought they did low damage. By the end of it they are doing 1d20 without any alterations. Most melee weapons don't do half that. My monks usually have a fairly high AC actually... Better than any other class I've done unless I went full out on Full Plate and even then sometimes.
The fourth. Okay quivering palm is bad. Tongue of the sun and moons can help for more roleplaying scenarios. Of course a wizard can just cast tongues.
The fifth. Well. It's so vague that it is meaningless.