I see people complaining mostly about lack of damage and survivability. but what about factors like:
diversity - the possibility to build a character in more ways than one. so while one player chooses to build a character all-physical, another one chooses to build them hybrid. a character that lacks this possibility (to a certain degree) IMO is psylocke, because even though one has the option play her hybrid or all-mental, the choices between the two is almost redundant. more so, psylocke's kit by itself encourages you to go hybrid, since the physical portion gains a bonus that the mental one doesn't.
theme - the identity of a character delivering upon its theme. an example for a character that I think doesn't entirely deliver on its identity is invisible woman. because even though I really enjoy playing her, and she's one of my favorite characters, for someone called "the invisible woman", I don't feel like I'm really exploiting her invisibility. I suppose maybe in the future this could be addressed to allow for various forms of invisibility (probably in the form of specs, huh?).
feel free to give your idea of what bothers you about characters. give examples too of why you think this character is lacking in a certain department.