Green Lantern has one fundamental problem when being adapted into a film, it's gonna have a budget. The thing that makes Green Lantern one of the best franchises in the industry is the fact that it isn't realistically inhibited in what it can do by money, and they can afford to do crazy creatures, like insane cats, and space elephants. Buy anyway I'm totally okay with them doing a GL movie as long as Geoff Johns writes it.
The way I see making this series kick ass, if they didn't have a budget, is to have them explain Hal and Sinestro's origins then throw in part of Secret Origin and have him fighting Sinestro. Then in the second movie do a version of Sinestro Corps War. Then for the final movie do Blackest Night
Green Lantern has tons of story potential whether they make it a sci-fi war movie or a more traditional superhero movie. They should have Geoff Johns work on this in some capacity. The secret origin arc hes doing right now could be tweaked a bit to make a great movie.