System Shock 2
And then, yeah, the brawlers and the shooters.
Metal Slug 3 actaully ain't that great in co-op in my experience. Of course, my experience has been playing with people who didn't really know what they were doing and all the weight fell to me. My patterns don't work as well in 2 player.
Another one that can really suck in co-op is Contra Shattered Soldier. Both you fuckers better be exactly as good and be on the exact same page, cuz the windows and timing stay the same, but enemy life is doubled.
I tried to play Contra SS with Dark10x once, assuming he knew what the fuck to do. I was inches away from S rank on solo, and he was still going through the levels dodging things. Soon as he blew the center of the first mini boss, preventing me from destroying all four arms, I flipped out and we haven't played again.
Edit: I also dig Time Crisis 2 & 3 in co-op. Nothing like getting triple my teammate's score and being an ass about it at every scene tally.