Every new big movie gets rated high at the beginning. The IMDB rating won't even be close to accurate until after the movie has been on DVD for a few months. Right now it's only fanboys and haters voting.
It isn't a score the movie got, it's a listing of how many reviews were positive vs how many reviews were negative.
If a movie gets 10 reviews giving it 3 stars out of 5 and 2 reviews giving it 1 star out of 5 it will be rated higher than a movie that gets 9 reviews giving it 5 stars out of 5 and 3 reviews rating it 2 out of 5.
after i look at the score i click on a bunch of the random published reviews from people who know movies and get their opinions. They seem to be much more insightful than some 14 year old fanboy who hates Michael Bay because Harry Knowles told him to.
the good critics go to movies with the intention to be enjoyed (Ebert for instance), though with most of the big releases they are disappointed because those releases suck.