Funny, I read a lot of negative reviews of First Flight, despite enjoying it myself. I will, however say, that Emerald Knights was even better.
First Flight does serve as a template of how to do a Hal/Sinestro movie with other GLs around.
Emerald Dawn II also shows how they could structure the next GL movie, as that comic had Hal teamed with Sinestro to further his training.
I think they'd be best served keeping Hal (sorry, but with him being forefront on the animated series and also pretty prominent in Young Justice, DC/Warner Brothers will push him) and starting the movie with a glimpse of the Book of Oa hitting the major points of Hal's origin, while leaving it somewhat vague as to whether or not this is in the same continuity as the first movie. Yeah, it's a blatant rip-off of The Incredible Hulk's beginning, but it would serve to get Hal's origin shown and allow the movie to start right away without being bogged down in the minutiae of whether or not this is a direct sequel.
That being said, I think they need to re-do Parallax. While the Earth stuff dragged down the movie, the Parallax stuff really took some enjoyment out of it. Perhaps, even leave out the Parallax stuff and find another way to introduce the yellow rings.