The methodology of reviews is fascinating to me. Oftentimes you'll find that some games get a pass for certain things, while others are thrown under the bus. There is a disconnect between pre-release chatter, and actual review scores as well sometimes.
As for the actual reviews, I basically only trust the opinions of a few reviewers that I've been following for years. As long as I have fun with the game, and the reviews don't kill sales, I really don't pay too much attention to them.
The 8/9 split is more of a function of the 7-10 scale that exists for games these days. It's more like 8.5/10 for AAA games. There is very little breathing room when reviewing a AAA title.