Green Lantern is a movie that I think that people overly critique with. Part of the reason is that all the talent from creative to the actors made people expect more, but at the same time it should not be getting worse reviews than other comic book movies that were bad standing with critics and the fans. I really loved it too but I think it was stupid that they did Parallax. It would have been so much better if they did a Manhunters arc with Sinestro having to show Hal the ropes that way you also get the development between Hal and Sinestro. And I think that was everyone's biggest problem: no one was developed outside of Hal. Yes he is the main character but the GL mythos has their supporting characters very well fleshed out so that is likely what bugged people also. As to complains about the CGI...I can't understand why people said it had shitty CGI (the design for Parallax was dumb to begin with so I didn't expect to like its appearances with the CGI so I'm looking at everything else). Some people thought it was dumb that he made certain constructs like the car and race track and the jets...but I'm thinking "is it really that silly and stupid? if it was just a bland construct that served the same purpose that would've excited you more?".
So overall, I enjoyed GL for what it was: a fun movie with a simple plot.