Though I love RTS games, I am usually terrible at them. Dawn of War is my all time favorite, but with a skirmish AI mod I have installed I get annihilated even on standard difficulty.
Gears of War online. Seriously, I'm terrible. I guess the main problem is I'm always paired up with people who know the maps and weapon locations off by heart so I never really get a chance to even learn the map. I honestly prefer playing it with bots anyway.
Battlestations: Pacific. I can't get my head round the control scheme and its confusing as hell, though to be honest I have only tried it out for about a half hour.