One of the hardest things in making a Green Lantern film would be which Green Lantern do you go with, since there have been like four of them.
1) Alan Scott (the original Golden Age GL; blonde guy, AKA: the Sentinel)
2) Hal Jordan (second GL from the Silver Age; brown hair, looked like Paul Newman, arguably the most famous GL)
3) John Stewart (third GL, black guy)
4) Kyle Rayner (fourth GL, dark hair; I last heard he was muscled out by John Stewart because John was being featured on the animated Justice League series and next I hear he'll be muscled out by the return of Hal Jordan)
Logically you'd go with the most current one, but Hollywood doesn't always obey logic [COUGH::Catwoman::COUGH]