People here on the boards, myself included, have mentioned that MGS3 is overrated for weeks. It's just that the Metal Gear Maniacs are so concerned about defending it that they flood threads about it. Where, people like myself who tend to think it's not as good really don't care enough to bother.
No one really "hates" the game. Most people can derive some quality entertainment from it. I just think that the series gets a free pass on things that other games get slagged for. It's a dinosaur in need of an ice age, but as long as it piles on the pointless rhetoric, over-the-top characters, and silly story they are willing to look past the issues.
People don't play MGS for cutting edge gameplay. That was proven by MGS2, which was a vast improvement in the gameplay department, yet was shunned by many because you didn't play as Snake. As someone who could care less about the characters in the series or its convoluted, downright comical story, MGS3 is an average game bolstered by impressive presentation.