Never on the internet, because I know what kind of backlash that leads to.
Seriously, though, I always find myself defending generally disliked games. Final Fantasy X-2 is always the first game that pops into my head. Sure the story and characters ruined everything that was great about the first, but it had one of the best (and most challenging, if you didn't over-grind) battle systems of the entire series.
Same deal with Star Ocean 4, the characters and story made me want to gouge my eyes and ears, but I enjoyed the gameplay and end game so much that I bought it twice.
I also find myself constantly defending the GameCube, which isn't a game, but I think it still fits in this topic.