IGN isn't an entity that has opinions. IGN's PS3 fanboy Greg Miller gave the game a 10. Honestly, the number is meaningless to me. I'm gonna play Uncharted 3, regardless of what scores that are posted on IGN, Gamespot, Joystiq, or 1up. It's probably a great game no matter what the reviews hyperbolize. I'm going to play it, and I doubt I'll call it overrated.
People have really deflated the meaning the word 'overrated'. I use it to say that something is bad but received praise. I'd say that Dead Island was overrated because it received good reviews and it was broken right out the box. People call Halo overrated, and that's one of the most well-built games I can think of off the top of my head.
It makes me regret my investment in gaming when people bicker about reviews. Form your own damn opinions. For the most part, reviews of AAA games don't have much effect on the sales. Marketing, on the other hand, does affect sales.
Does Uncharted 3 deserve a 10? I'll have to play it to find out, but I've loved Naught Dog games since Jak & Daxter The Precursor Legacy.