I don't think I read enough contemporary fiction to make sweeping, definitive statements about it. So I won't say that Extremely Loud and Incredibly Close is the best book of the 21st century so far. But I will say that it's the best book I've read so far this century, and that Foer belongs in the rarified category of contemporary greats like Phillip Roth and Kurt Vonnegut.
This is not a perfect novel; it gets a little (but just a little) gimmicky in spots, and there are times when you just wish Foer would tell his story and get on with it. But the overall effect is amazing. Oskar Schell, the pre-pubescent protagonist, is one of the most memorable characters in all of American literature. His quest--to find the lock opened by a mysterious key he finds while moruning his father's death in the 911 attack--takes him all over NYC and into contact with a host of striking characters. Interwoven along with Oskar's quest are two other epistolary stories that reminisce on the Dresden bombings and the regrets of a life shattered by trauma.
Extremeley Loud and Incredibly Close reads like an attempt at salving the wounds of 911, but it's more than that. It's a meditation on survival and hope. And it's not nearly as hokey as I just made it sound.