Good points... 1. It stuck fairly consistently with the mythos of the origin and Planet OA; 2. Ryan Reynolds did decently as Hal Jordan (though he fits more with the Kyle Rayner/Guy Gardner type than Jordan) -- but I wish he was more serious; though non-GL fans couldn't care less about this; 3. Blake Lively was eye candy; super hot, but not much else; 4. Green Lanterns Tomar Re, Kilowog and Abin Sur were damn good but didn't have enough screen time to be significant; 5. Mark Strong's Sinestro was excellent! 6. Hector Hammond was well portrayed by Peter Saarsgard (though it lacked a proper finish) 7. Good supporting cast from Tim Robbins (Sen. Hammond) to Angela Bassett (Amanda Waller); 8. Green Lantern's costume was wicked; 9. Visual/CGI effects were pretty good
Bad Points... > It tried to fit too much into one movie, moving back and forth from Earth and outer space/OA, thus there was no proper flow... (like when there was a build up of momentum, things go slow or boring; or from serious to funny without proper pacing); too many stories were crammed into one movie > Humor was misplaced at times (good peg is Thor which had it in the flow rather than contrived/forced) > Parallax looked comical; scary at times but only a couple of times > Like Iron Man 2, I wish the fight scenes were so much more; they spent too much on the set-up that the fights were short and could have been so much more and elaborate. > Some scenes and even some characters were not necessary (Hal's best friend, even some scenes with Blake's Carol Ferris were not needed); they should have added more action instead
Summary, visual effects, actors, GL base story good. But the way the writers and director put things together were a mixture of various plots and subplots crazy glued into one movie for pure entertainment. Kids will enjoy it, but adults likely will not. This is a summer of superheroes, with 3 down and one more to go (well, technically 5 with Transformers if you're thinking comic book stories), so it's quite impossible not to compare them to each other.
The director is known to direct good flicks like Goldeneye and Casino Royale (two good movies), but I wish he did more; studied more, had split up more stories to be more single- minded and not work on a cluttered material.