I actually saw GL Monday night. Me and a buddy went to the only theater in town (and it's not a big town), and we were the only people at the showing. :) Saw it in 3D, and they did a nice job on that for the most part, but I never feel like it makes an enormous difference in my viewing experience.
I thought Green Lantern was pretty good - certainly a fun super hero movie. And if you were a fan at some point, you'll probably enjoy it. You'll like seeing some of the "best known" of the Corps like Kilowog and Tomar Re. It's got issues, and you might not want to think about some things too hard, but it's fun.
(Full disclosure: I actually own and wear a GL ring that I had custom made by a local jeweler. So I think of myself as a fan of the character. But that's a double-edged sword for a movie. I could easily have been pissed off by it BECAUSE I'm a fan of the character, and I wasn't.)
I actually just got back from this an hour ago. I thought the movie was great really, though someone really needs to tell the movie industry that this 3-D shit they're advertising sucks alot. The movie was well done, no dull points, and cool CGI and fight scenes (all 3). Ryan Reynolds does a great job as always, between his snarky wit and lighthearted sarcasm, he's always enjoyable to watch. However, Sinestro get's the award for being just too awesome for a secondary role. Mark Strong stole the show honestly, his role was more demanding then they gave him room for. Yes, it's about as true to the comics as any other comic film, but it's a good movie, not a faithful recreation on film, who would really want that.
As a matter of fact, why is it every time someone watches one of these movies (comic book film, video game movie, etc), they always expect it to be the same as what they watched on TV or read in the comics or played as a younger person? If you want to watch Dragonball Z the anime the move, go watch the anime on DVD, you'll like it better. When you watch a movie, stop judging it on how exact the recreation is, that's just boring. It's why you get shit like The Last Airbender (when you really get down to it, it was season 1 in 90some-odd minutes but dopey looking). Shoot me if you like, but I enjoyed Dragonball the movie, it was an entertaining romp with characters I recognized, not a spitball at akira toriyama's creations (cough*GT*cough). The X-men movies were all great (3 pushed it a bit), the Spiderman flicks were well done (3 wasn't so much, but eh), Mortal Kombat was hillariously awesome (that song was great, you know it), and so on. Look at every one of these movies, and you see something you recognize, but different as well. Yeah some of em suck, but alot of movies suck. I mean shit, The Fast and The Furious was an awesome movie, then they fucked it up 3 more times and got the fifth one good again, shit happens...alot.
I recommend Green Lantern, it is worth the 11 bucks (don't buy the 3-D shit, not worth it). Up next, Transformers (yeah, that was respectful of its anime and cartoon origins alright, LOL).