Metroid: Other M, Hey You Pikachu, Lost Planet 2, Dead Island, and MW3.
I bought all of these games thinking "zomg, this game is going to be so AWESOME!" but then slowly realized it is absolute shit.
For Lost Planet 2, the "absolute shit" moment happened after about 20 minutes of gameplay. For Other M, after the third time that horrible excuse of a Samus opened her stupid fucking whiney ass mouth. Hey You Pikachu after an hour or so, I can't remember cuz it was a very long time ago. Dead Island, either after about 8 hours and realizing I am nowhere near completion or a point where I can hold my own, or when I tried online only to realize that playing with randoms is like playing with randoms in WoW... only worse... MW3 after my 2nd prestige I think. Thats when the servers went to shit, and I realized how much fun I could be having by playing Skyrim.
Edit: I also bought Duke Nukem Forever knowing it'd suck, but thought "It can't be THAT bad".
LOLOLOL was I wrong...