When I first began to play CoD4 I loved Bloc because it was a sniper whore map and I was a stealth spec ops--mp5 navy, claymores, usp with silencer, extreme conditioning and UAV jammer--that would stick to the perimeter of the map and just knife and shoot all of the snipers. Leaving a claymore here and there in a few well traveled pathes and sniper perchs as a friendly hello. Now that I've finally made it to Prestige I'm trying to stick to rifles and sniper rifles instead of mainly smgs. It's almost as much fun sniping people as it is trying to foil the people trying to get at you In Bloc. Martyrdom and claymores make it easier though, man do I miss those perks.
I played FPS's online for years--mainly Medal of Honor Allied Alliance, Day of Defeat, Battlefield 1942, Road to Rome, Secret Weapons of World War II, Counter-Strike: Source and Day of Defeat Source--and so far I don't think that any CoD4 map is badly designed or really balanced in the favour for any one team the way a CSS map would be for example. Personally I think all of the CoD4 maps are all really fun to play on, yet all I hear is "this maps sucks", "this map is gay", etc. when Bloc, Downpour or Pipeline show up as the next map.
Sometimes I do get sick of a certain map, but that's just because the hosts keep ending the matches mid-game, some are kind enough to end it in the lobby or there's a spat of server connection errors and I play the same map five or six times. Then I cast my vote to skip a map.