A lot of characters mentioned are more the victims of lazy writing than anything else. It's a shame many of them could have been interesting if the writers didn't make them Mary Sue (Wesley C. and Seven of Nine) or having their character being a victim of autopilot(Harry Kim, Chakotay).
Wesley Crusher could have been interesting by having an equal number of disasters and "so whats?" to his brilliant saves. I am one of the few posters that doesn't seem to have Wesley Crusher Derangement Syndrome.
Seven of Nine would have been more interesting if we were never sure if she had left The Collective for good.
Neelix and Deanna Troi are slammed for stating the obvious. Spock did this as well(very few slams against him for this)
Kes and Jadzia,IMHO, were wasted opportunities. This was no fault of the actresses. The Trekverse had a chance to explore truly alien races. One was a species where the height of achievement was becoming one with a what we would term an intelligent parasite. The other, a race that lives about as long as a Great Dane, but has untapped mental capacities. It might have been better to pair Tom Paris with Kes. It wouldn't have sucked out Seven's oxygen at all. Jadzia, it was a pity they let her go.
Chekhov seems to be cited as most annoying in TOS. I was a little kid and liked him because he had the Beatle/Davy Jones haircut. I still do.
I know I made a short story long. The fault lay with the writing decisions.