Re: Thor's box office competition - Part 2
I've never read the comic, although I've read JLA comics including GLs, and seen the various cartoon series that included a GL character. To be honest, I would think you could follow it easily so long as you grok the basic concept of what Green Lantern is, and what his powers are. Even if you've only mainly read Marvel comics, you're used to the conventions of comics superheroes, so it shouldn't be difficult.
The movie itself opens with a (IMO) clunky prologue that flat-out tells you the background of the Green Lantern Corps. (I thought it was even clunkier than the background dump at the start of Thor -- which the script at least then framed as Odin telling the story to Thor and Loki as children, which excused it for me a bit.) The rest just isn't that hard to grasp, and there are several other "we're just going to TELL you" bits.
The parts that may confuse you are parts that are going to confuse a lot of people, because of poor scripting and editing choices.