Underworld was a bad movie. The first few minutes were good, then it went into a terrible downward spiral. You may not agree with that, but that does not make the opinion of multiple critics who panned it wrong. I haven't seen Benjamin Button, but I can imagine the critics calling it Forrest Gump 2.0, and therefore not as good as some of the other more original films.
Metacritic (or Gamerankings) as a measure of quality may be flawed, but it sure beats most other ways of judging video games. For me, these sites provide a very valueable starting point with which to begin weeding out the wheat from the chaff. Once I have a list of potential titles to consider, I then read the high and the low reviews for each before I make up my own mind.