Please, the critics can't really be trusted much with a franchise like Final Fantasy any longer. The latest ongoing trend (past few years) is that a game has to be innovative to score high, while a game like Final Fantasy, where you know what to expect for the most part (gameplay terms), the enjoyment factor depends on the story.
I won't say that FF XIII is the best game this year, and I haven't - nor will I be able to play it for quite some time. I just don't quite trust the critics on this one, because it seems they've burned themselves on FF XII and want to play it more safe this time. FF XII was a flop in my eyes, though it received an average meta score of 92% (user rating 78%). FF XIII has currently a meta score of 83% (user rating 85% - too early to be reliable, but it doesn't seem like many were disappointed).
Just to bring some of the data to light, EDGE (pretty renowned game magazine) gave FF XII a score of 90/100, and *shock* FF XIII 50/100. There can't really be that much of a difference between them, and I'm fairly sure XIII is better than XII. Critics got burned, got angry, revised their scoring systems for J-RPGs. I'm sure XIII is great if you like the genre and the story gets to you.