For me, it has to be:
Uncharted 2: It brings cinematic gameplay to a whole new level. The whole experience is so goddamn smooth and perfect, from the amazing controls, to the fun story, and the transitions in between. It also really blurred the line between what would normally be delegated to a cut-scene, and what you actually got to play with some of its amazing set pieces. Truly the best experience and my favorite game this gen.
Red Dead Redemption: Ever since I was 10 years old I've wanted this game. An open world cowboy game full of ambiance and atmosphere that just sucks you into the world and makes you not want to leave.
Metal Gear Solid 4: The concept of "stealth in the middle of a battlefield" was executed perfectly in this game (well, the first couple acts at least). The amount of details, ways to approach levels, and epic set pieces make this one hell of an experience for me.
Some standout moments I remember are tracking Naomi through the woods after the Laughing Octopus battle, realizing on my second play through that the robots in the trench coat actually follow you through the whole level of Act 3, the crying wolf sniper battle at Shadow Moses, Metal Gear Rex vs Ray, and, of course, microwave of death.
LBP: Awesome concept, awesome execution. I've spent soooo many hours playing this game with friends and discovering awesome levels, and it never fails to put a smile on your face.