I'll just break it down by games I play:
Halo 3: Standoff and Rat's Nest. They are just dull maps, especially in Team Slayer. Standoff, in particular, is just a stalemate till one team gets a Warthog breakout, then the other team is probably pinned till the end of the game.
Halo Reach: Sword Base. It has one completely dominating position, rendering 90% of the map pointless. You basically have to take elevator if the other team has it, because they certainly won't come to you. And if you attack, you are guaranteed to take casualties. Its just a huge mess.
Team Fortress 2: 2Fort. For reasons stated in this thread, its just a boring map. It'd be more fun if people actually tried to win it, but so many people are more than content to camp as Engineers and Snipers, and any push always fails do to a lack of attackers.
Modern Warfare: Creek. Ba gawd, Creek. Far too busy visually, and 90% of the fighting happens on 20% of the map.
World at War: Dome. MP40 paradise
Modern Warfare 2: Karachi. No particular reason, I just didn't like the map. Never did very well on it.
Black Ops: Hanoi. Its got the worst spawns in the game, and its got a sprawling and unintuitive layout. Just a boring map in general, with lots of frustration to boot.
Bad Company 2: Panama Canal and Attacama Desert. Way too big to be a conquest map, and full of snipers. Boring to play on, and the matches take forever.
Left 4 Dead: Blood Harvest. I dunno, its just a tedious map to play.
Left 4 Dead 2: Swamp Fever. Impossible to get a good attack in when playing as Infected. The first two maps are basically gimmes to the survivors if they have half a brain between them.