It's Resident Evil 4, but that's no disrespect to Uncharted 2 which I cannot stop playing.
RE 4 re-created a dying franchise and evolved it into one of the greatest games of all time - possibly the best game of the decade. While I believe Uncharted 2 will win my GOTY and many others as well, and is one of the best games of the decade, RE4 is just a little better.
That said, UC2 is absolutely unreal. It's like picking between having 100 dollars or 99 dollars. You'll pick 100 dollars, but if you had to pick 99 dollars, you'd have 99 dollars, and be able to buy almost anything the guy with 100 dollars could.
Sorry for the stupid metaphor, but really, both games are genre defining and top 5 games of the decade - RE4 just did it first.