In their introduction, they clearly state that they don't take into account the review scores. And regardless of their influence on the industry, they're still human, they can get it wrong sometimes you know. What I find funny is that you say they're wrong simply because they have a different opinion, as if yours was so perfect.
http://www.ign.com/top/modern-games/100
Apart from the fact that most of these games I've never even heard of, I fail to understand how RDR is better than GTA IV, how Half-Life 2 Episode 2 is mentioned and Half-Life 2 isn't, or how games like Alan Wake or Heavy Rain appear here when they aren't even f*cking games!
These games were clearly picked based on one criteria: IGN's fanboysm. Everybody knows they get an orgasm each time they hear ''Mass Effect''.
Oh well, at least they forgot Halo.