tl;dr It's bad. Not as bad as other movies I've seen recently, but really, really not worth your time.
Green Lantern - space cop, camp costume, aliens, ring which projects solid green light. It's an incredibly silly concept, but it's one that also works damn well. I've been reading the comics and, on the whole, I've liked what I've found. Sure, the man masterminding it all - Geoff Johns - has his drawbacks, but he's a great storyteller. Without the strength of his storytelling some of the rather more questionable aspects of GL and his own take on the mythos end up rather dragging the story down.
Take our protagonist, Hal Jordan. A playboy, a fighter jet pilot, a hothead and something of a man who has a problem with authority. Got daddy issues too. In other words, insufferable jerk. Yet in the comics we can sympathise partly because he does possess some sort of humility, and partly because he still has a vulnerability to him that offsets the inevitable over idealisation of such assholish traits. Well, being a pilot doesn't make you an asshole, but you know what I mean.
So despite his archetype, in the comics Hal Jordan is deep enoguh to be likeable; give Hollywood this archetype, however, and the reward is just simply insufferable. His daddy issues are brought up and then dropped. He has an incredibly phony scene with his young nephew, a hamhanded attempt to make him more relatable. People who are the victim of his hotheadedness are dismissed as violent thugs, and the same hotheaded behaviour, it is concluded, is what makes him special. Development happens, but it's shoe horned in and never has any real substance. Towards the end he reveals, apparently, he does feel fear and then lots of heavy-handed speeches occur telling him to conquer it. No prizes for guessing how successful he is.
Really, it's the structure of this movie that lets it down. Many of the reviews I checked out theorised that a lot of scenes had been cut, and this would make a lot of sense. Things are not introduced properly and the three main subplots develop without any decent connections to each other. Central to the story - arguablely, as it is really unclear - is the relationship between Hal and Carol. In a special effect driven space opera, the entirely earth bound romance is what the movie takes the msot time over. The subplots involving the Lantern Corps struggling against giant space entity Parallax, and evil psychic biologist Hector Hammond researching aliens are both shoehorned together.
But if the romance is good it can work, right? Sure, if the romance had been good, the story may well have worked. It wasn't. It was dull and underdeveloped and there was a painful lack of chemistry. Neither of the actors lent the relationship much credibility. Carol's characterisation - one minute towing the rival line, next minute the love interest - was incredibly inconsistent. Like everything else in this movie there was no flow to her character and this really hindered the relationship.
Aside from Carol, probably the next character with the most screentime, and even less consistency, is Sinestro. He comes across as the leader of the Corps, aside from the silent and Yoda-esque Guardians, but this is never really confirmed. At one point he decides he dislikes Hal and starts beating him up. Then, later, he is not so harsh on Hal, after Hal quits the Corps.
I would criticise Hal's quitting, but I'd repeating myself. It's poorly established, badly explained. The real villain here is the film's structure. Nothing is properly grounded and there is no consistency. It's probably clear by now just how much of this film didn't work, so here is what did work:
Hector Hammond was the best character here. He feels shoe-horned in, sure, but his motivation is the best established and the connection he and Hal have is the one that feels the most genuine. Hell, the best scene in the movie happens when the two of them first battle. It makes no sense that Hal would know to interfere, sure, but it is genuinely an intense scene.
The whole idea of space battles is awesome. What we get of the action in that department is rather mixed, admittedly, but nonetheless it is conceptually very cool. Space evil cloud thing Parallax actually looks rather impressive too, carrying a real gravity to him that never really comes to fruition in the plot.
This is a pretty bad movie. It has bad acting, bad directing, bad editing, godawful writing...it's not the worst film I've seen in the cinema as of late, but damn. This had promise, too. I know from first hand experience that there are great stories to be told with this mythos, with these characters. I expected something derivative and lacking in creativity when I went into the cinema, but what I got was properly bad. Bah.