One of the first things is this is not a straight adaption of the comic, while there are many elements here, there are also certain things that weren't, some just didn't translate well to film so they weren't included. There are also some changes to the origin of Green Lantern Hal Jordan, this film is in many ways an origin story, for example Parallax defeating Abin Sur before he crashes on earth is not the original origin. But I don't find these things to be a major issue as long as the film is enjoyable, which I felt it was. Because this is an origin story is does take a little bit to get going but once it does it moves along at a good pace.
Some scenes, particularly the fight scenes and training scenes may seem a little short but they do show enough to get the point across, yes I do wish they were longer. The CGI was done very well despite they worked on it till the end, Oa looked amazing, but the 3D could have been a little better, it seemed a little blurry and out of focus at times. The story was told well and got a lot in in a short time frame, 1 hour 45 minutes.
Some may not be happy with how some scenes went, the romantic ones for example seem a little too much, but they are a necessary evil in a film of this type. Mark Strong as Sinestro was easily the best of the main actors in the film in my opinion, he played the role the way most will hope he would have. Most of the other actors, Ryan Reynolds, Peter Sarsgaard, etc., were pretty good although not prefect, Blake Lively was the weakest but she was decent as Carol Ferris although a little uneven at times, I'm curious to see how this may play out in a sequel(s).
The big after credit scene (possible spoiler) was a little rushed as a fellow movie goer put it but I did feel it fit into the film the way it was done. I can definitely see them making a sequel, there is way too much to explore in the Green Lantern universe not to.
Overall I feel the movie was a solid 4 of 5 stars, not the best superhero movie ever but far from the worst and better then many. If you haven't seen it you definitely should (in either 3D or 2D) it is worth the price of admission.
Thank you for reading and enjoy the movie if you haven't already.