This is probably hilariously the only time I've seen a poll thread that has more responses than it does poll answers. OP, you dun goofed at making those options. Where's Halo? Killzone? Resistance? Star Wars: Dark Forces? Doom? Quake? Borderlands? The Darkness? Star Wars: Republic Commando? Deus Ex? System Shock/Bioshock? Half-Life? Portal? Left 4 Dead? Serious Sam? Duke Nukem? Wolfenstein? Team Fortress? Counter-Strike? Crysis? Far Cry? Unreal Tournament? Metro 2033? S.T.A.L.K.E.R.? Timesplitters? Heretic? Hexen? Or at least an "Other" option so people who want to pick those, can.
EDIT: There are a lot of first-person shooters, man. I even forgot Tom Clancy's Assorted Games, which is something like three or four different series', Star Trek Elite Force, and F.E.A.R. Or how about Shadowcaster, which is probably a game that nobody on this website will remember even if they've heard of it? Though I guess that's more RPG and less shooter... well, Fallout 3/New Vegas too then.
As for myself, dunno what I'd be able to pick. Maybe Deus Ex: Human Revolution or Crysis 2. Or maybe the Halo series as a whole, or the Star Wars: Dark Forces series (from Dark Forces to Jedi Academy, of course).