Biased against -
RPG (both western/eastern/whatever), RTS, management simulations, or basically anything that is boring and has more to do with moving icons and clicking a button than actual dexterity or maneuverability
Horror games - it wasn't until recently that I realized how little I like the genre. The stories and characters are usually good, the graphics and music are usually terrific, but the combat in these games is always clunky, and the puzzles have gotten to the point of being downright bizzare. How many times do I have to move a bookshelf to find a book that has a small statue inside and then find the corresponding small statues and put them on a scale in the main lobby? Better yet, why would I even want to?
game company stupidity - if a company makes a string of dumb decisions that affects the quality of their games, I tend to stop caring about what they release. Most obvious examples would be whatever the story was with DMC2 (I believe the game director was some former famitsu writer that had never actually worked on a game before), the complete dumbing down of DX2's biomod and inventory, and most recently, id software's focus on showing off a lighting engine rather than making a game that's actually fun to play.
Biased towards -
PC online gaming - I still find UT2K4 and the dozens of mods available for it to be more fun than any online console game. The fact that you don't have to pay to play online and get
gigs of content for free helps too.
SCEA Platformers - other than the Jak series which is really run off the mill, I find the platform games that Sony has published to be more fun and have higher design quality than a lot of the other garbage out there. Super Mario Sunshine was good but I think Insomniac is pushing the genre forward far more than anyone else at this point.
Established developers/franchises - I find "Killzone vs. Halo" or "Forza vs. Gran Turismo" arguments to be hilarious because you're comparing new franchises from unestablished development teams to some of most successful games of the past ten years that continue to attract new fans. Even if a new development outfit consists of people who have worked on good games, they haven't done it together yet. Once in a while you'll have a team like Valve or Retro that really hit it out of the park on their first swing, but that doesn't even happen on an annual basis. I just don't see the point in comparing question marks to definite, must-have purchases.