Hawkman. No other character's history has ever been this badly mangled.
Donna Troy. Misused, abused, and stupidly killed off.
Batman. Starting with
DKR, he lost all his humanity and warmth, becoming a hateful, one-dimensional psycho with no redeeming qualities. Some writers have tried to correct this, but overall the more one-dimensional and slimy Batman is, the more fans seem to like it.
Superman. Starting in 1993, the character started being eroded by half-baked non-"events" and bloated, linked soap-opera crap that ignored him infavor of a massive supporting cast compromised of ciphers. Then we got the beginnings of Lois Lane, Superbitch, which carried over into the current comics where she's gotten WAY out of hand. Then Superman's intelligence, courage, and confidence took a walk, replaced with cowardice, being pussywhipped, and emotional instability. Add to that the creative, editorial, and corporate stagnation that took root as of '93, and you have the poster boy for seriously screwed-up comic book heroes.
Spider-Man. The whole "Clone Saga" did nothing but put a huge black mark on the character that will never really be erased, and the constant jerking around with his marriage made it even worse. Yeah. JMS has him and MJ together now, as they should be, but will it last? Judging from past history, I would say no.
Black Cat. When we last saw her, she was on the verge of being raped. Oh, yeah, GREAT way to leave a character.
The X-Men. You'd need a scorecard to list out all the stupid stuff that's been done to the characters.
Iron Man. The whole teenage Tony idea was BEYOND retarded. Wouldn't it jsut ahev been easier to have Tony be brainwashed by Kang and subsequently struggle to redeem himself than to kill him off and bring in a time-displaced teen version of himself?
Aquaman. Nobody knows what to do with him. There's no direction to him at all.
Wonder Woman. Perhaps the biggest victim of the Crisis. Her romance with Steve Trevor? Trashed needlessly. Her Diana Prince identity? Given the heave-ho. The supporting cast Marston gave her? Scrapped and replaced with a ton of Johnny come-latelys. Cheerful and amiably cocky persona? Replaced with a tiresome, boring deer-in-the-headlights perspective on everything. Add to that the very annoying tendency she has toward hitting on married men (Superman, Aquaman) and going thru boyfriends like Kleenex (including some superheroes, to boot), and you have a character who's been reduced to a boring mass of Silly Putty with no direction, no style, and no core. She's basically just a writer's fantasy plaything now, which is a shame.