If it's crap ... We'll tell you
One of the evil lantern corps I guess. Start with Sinestro and the founding of his corps. The second movie could be the Red lanterns, and introduce the Blue Lanterns as allies. The third one could involve the Black Lanterns and all the Lanterns uniting against them. That would be how I would escalate a Green Lantern trilogy.
Beyond those I don't think Green Lantern has many good villains. The Manhunters might be interesting though.
I should also make note that I do not read the comics. Most of my knowledge comes from cartoons and stuff I've read online. I will say there is a cartoon called Green Lantern First Flight which I really liked. A new movie should take some pointers from that and rework it to make a good first movie. It gets into space real quick and sets up Sinestro as a great villain. I will admit that it focuses more on action than fleshing Hal out as a character though.
I like Diatribe's ideas leading to the Blackest Night (although actually adapting that story to screenplay would be nearly impossible), but if you're going to reboot the entire series, I feel the villain should be Atrocitus. His motivations and origins aren't that hard to explain, and having him as the villain could help set up not only the Red Lantern Corps, but William Hand as well (should they go with the "Secret Origins" story arc).
As a Green Lantern fan, I would love to see Krona on the big screen. However, what you have to take into account is what we WANT to work in the screenplay, and what WILL work in the screenplay. I personally feel that Krona's origins and motivations are simply too complex for the typical movie goer (and by typical, I mean someone who doesn't know a damn thing about the DC Universe).
So again, while I'd like to see Krona, I don't think he would translate well to a screenplay. I think we'd be better off with Mongul or Carol Ferris/Star Sapphire over Krona.
Agreed, and they tried to do that with Krona in the previous Green Lantern film.
..... They turned him into Parallax. *facepalm*
Look to this animated series (that just fucking got cancelled) for a reboot, it's been great
I'd like to see a straight up sequel!
just give the franchise to Christopher Nolan he seems to be killing it with batman and superman