Text based games. No matter how many times I've tried, I just can't play Zork. Guessing at which combination of words will find both valid, and correct gets extremely old. "You see a hammer." "Grab hammer" "Does not understand 'Grab'" "Get hammer" "You get a hammer" "Hit head with hammer" "You suffer extreme damage from hammer" "Hit head with hammer" "You are dead". End of game. Any other genre I can't say I've never gotten into. FPS, 3rd person adventure or shooter, strategy, real time strategy, they've all had games I've enjoyed. Hell, Gran Turismo 2, Wrestlemania, and NFL Quarterback Club 98 were fun games. I can get into any type of game as long as it's made well, and almost any genre can be made enjoyable.
To go along with the thread, I've found myself less and less likely to enjoy a JRPG. The constant level grind gets old very quickly, and it's all the same story. Most FPS games have the same story, evil bad guy/group does something evil and you stop him. With JRPGs it's evil bad guy/group does something evil, you spend 40 hours hitting rats and birds to gain levels to stop them. It becomes very tiresome.