Stealth. I mean... I really don't hate stealth games, but I always become bored playing one. More then 75% of the time, I won't start the game up more then 2 times. I was able to thoroughly enjoy Splinter Cell: Conviction though... for whatever reason.
I'm currently in the process in trying to get into Metal Gear Solid. I absolutely love the humor/style of the series... but I'm really not having fun with the gameplay. It makes me sad. :(