I think it's the complete opposite. They rate games much too high. They're basically a hype machine. Example:
I really liked Uncharted 3, but once I finished it, I said to myself: "This really didn't deserve the 10 it got from IGN." Controls were much worse than in U1 and U2 - having replayed through both just before U3 came out, I found aiming to be really bad compared to the other games, especially pulling off headshots, storyline didn't quite work since it raised tons of questions the game never answered and two characters get kicked out of the story halfway through for basically no reason, the villains' motivations and true identity are never really revealed, etc. Yet none of those things are mentioned in IGN's review.
Mind you, this might only be Greg Miller's problem, since most of the IGN reviews I have problems with are his. His Dead Space 2 review still makes me laugh and cry at the same time. It looks like a nine year-old wrote it.
At IGN in general, from what I can gather, if a game has good production values, it gets a dithyramb, an insanely high score and free PR for the publisher. If it has subpar production values and/or is a different experience to most mainstream games, it gets shat on and lit on fire.
Personally, I mostly use Destructoid and GameRevolution for reviews, then watch GameTrailers' review to get fresh video footage. Then I typically have a good idea and can make a decision whether or not to buy the game.