I loved it! Not as good as Iron Man, but a great flick! During the opening monologue, I realized that the film might get a bit confusing if you didn't already have a passing familiarity with GL, but maybe not.
I was convinced the costumes were going to suck, but I actually liked them. Still too CG looking, but the glowing costumes were fun. The ring constructs were awesome! Parallax was a much more frightening "monster" and better designed than the comics version. I thought the story was good, but yes, it was light on character development, although you got enough to understand the film. I enjoyed the acting, with the exception of Lively (Carol Ferris) who was a bit wooden.
The world and character design was inspired and a fantastic reimagining of the GL mythos. I especially enjoyed how Parallax was a blend of Parallax from the comics and the corrupted Guardian Krona. They even foreshadowed it well by the missing and broken seat at the Guardians council chamber.
All-in-all, it was great!