What they wrote about it outlines exactly what's wrong with the review they (And a few other sites, it seems) put up.
"Was it worth the wait? For ardent fans, undoubtedly. For everyone else, however, we really have to wonder if Polyphony Digital understands that it ultimately painted itself into a corner. The expectations placed upon Gran Turismo 5, built off the back of years of waiting, refining, teasing, rethinking, hyping and overselling ultimately took its toll."
They weren't really reviewing the game itself. They were reviewing the game against the expectations they had.
In a way, I suppose it's Sony's/Polyphony's own fault for hyping it up to be the 2nd coming of Jesus, but seriously... Some of these reviews are plain stupid. Even in the IGN review the reviewer stated that it was by far the best racing simulator he had ever played... Yet he still felt the need to give it an 8.5?
AND! I have to complain again. They also listed Pokemon Heart Gold/Soul Silver as a disappointment? WHAT!? I am beginning to lose all faith in IGN.