Since I always get main-stream stuff, this is going to be pretty hard.
Worst ever: Bad Dudes
RPG: Neopets
First Person Shooter: Chex Quest
Fighting: Mortal Kombat
Action/Adventure: Metroid Prime: Hunters (Well, they expected me to call it an adventure game, even though in that aspect, it sucks.)
Sports: I never played any sports games but one. Can't compare.
MMORPG: Runescape
Racing: Sonic R
Action: Bad Dudes
Puzzle: Mr. Driller: Drill Spirits