Considering how much fanbases are invested in the games and the impact the score makes on the sales... if I were a reviewer I would avoid reviewing games for genres I don't like... I know Halo is fantastic, but I don't like the type of game, so my 70 wouldn't do justice even if it was my sincere analyse.
I disagree. Critics aren't here to tell fanboys what they want to hear; they're here to inform. A well-written and informative review -- positive or negative -- will tell you if the game is right for you.