From that list, MGS4 was the game that most blew me away. L4D I could leave, although the multi-player was awesome. LBP did lots of cool things, but it failed to blow me away, or attract my long-term attention (although my daughter and wife still play it a great deal), F3 is awesome and totally up my street, but just not as good as MGS4 imho, and GTA4 disappointed me on a slew of different levels, although it is an awesome game dispite its flaws (no, not a 10, but certainly a 9).
So, for me, in order:
1) MGS4
2) F3
3) LBP
4) GTA4
5) L4D
Further, for me, Valkyria Chronicles should be up there above GTA4, but I admit not everyone will love that game the way I've learned to.
That all said, I wouldn't be surprised if it was F3 that won purely because it has multi-plat appeal, which isn't good as a reason, but is understandable.