You know, for a story of such intergalactic peril, it's hard for me to remember anything of significance. The movie is literally slipping from my mind, but I'll do my best to diagnose the film.
The Good: The Green Lantern planet of Oa, and the power ring effects are pretty. The performances aren't bad. Ryan Reynolds is a good actor, even though he wouldn't have been my choice for Hall Jordan. Peter Saarsgard is also good as Hector Hammond, and the film would have benefited from more of him. Whenever Mark Strong appears, I feel like caring. There's a training sequence that is easily the most entertaining thing in this film. Mark Strong just has a gravitas and an intensity that the movie needed more of. That's not to say that the rest of the film is full of laughs. It's not. Humor would have also added a lot to the film.
The Bad: About that lack of humor. I'm going to blame most of the faults in this film on the writers. Nearly all of them have only written for television. They've all produced more than written, and two of them have written for No Ordinary Family and the bad half of Heroes. Oy. To quote the Mythbusters in a pseudo-plumber voice: "Well there's your problem." There are a bunch of superfluous scenes and some fairly random cuts to unrelated stories scattered through the film. Nearly everyone mentions Hal's dad's jet fighter fatality to him at least once, just to make sure we remember. Then there's the problem that the audience is supposed to believe two test pilots, a senator, and biology scientist all know each other stretching back to childhood or are related. And two of them receive superpowers. It's not like this is going to ruin the film. It's just another thing that subtly tells you someone wasn't trying. And that's the gist I get from this film.
The film basically has no real antagonist. There's a floating cloud of blackish-yellow Parralax doom, but it never really poses a threat. It's kind of laughable that Hal Jordan travels to Oa and back to Earth twice before Parralax could conceivably reach either. Thank goodness when it gets to Earth it attacks the half of that planet that's in broad daylight, or you'd never find it. Hector Hammond should be a better nemesis, as he has telekinesis and telepathy and an actual personality, but the film spends too much time trying to make him sympathetic rather than a true villain. He has no real scheme or goals, he's just a victim of Parralax. I know the reason the filmmakers went with these two sad sacks is they want to save Sinestro for a sequel, but judging from the box-office returns (only $50 million on the opening weekend? for shame.) they should have hedged their bets and spent that rainy day money early.
Because there's no real villain, the problem Hal faces is...self doubt. How exciting. He has substantial fears, which is exactly the sort of thing I would think should probably disqualify someone from being a test pilot. Anywho, I think Hal's real problem is a lack of imagination. A minigun, chainsaw, and a couple of jet fighters are the most interesting things Hal does with the ring.
The Ugly: The film has a drastic overuse of CGI. Green Lantern should at LEAST have a real honest to goodness costume. Superman's from another planet too, but his costume is made of honest to goodness cloth. It's hard to really be interested in a hero when 85% of his body is digital. And when his power is to create green CGI from the power of will, there should be more creative uses than what we see. What should be Hal's iconic entrance into the public eye has him instead - I kid you not - rollar skating a helicopter through a series of Matchbox Car-style loops to safety. Like a Cartoon. I think Daredevil slicing a man in half with a subway train was a better superhero introduction. Even the characters later admit how stupid and un-iconic an introduction Green Lantern's display of power was, which means the writers probably also knew.
Bottom line, the movie is ho hum. There's just no wow factor. Aliens and power rings and telepathy seem to faze almost nobody in this film. And if they're not interested, I'm not interested. There are few moments of power, depth, or interest or anything. Therefore, I give the film a D+