(Note: I usually try to stick to some established points in the real film. Where I feel I need to make a note, I'll do it in brackets [like this] because I might use parentheses for other things. Reading these, it will help to see the movie in question. Otherwise, you might be confused. And of course, spoilers of the actual film will probably run rampant.)
Young Hal, Young Carol, and Young Hector are all at the airfield. Festivities. Young Hal speaks with his father while his friends are somewhat behind. Hector tries to catch Carol's eye, but she only has eyes for Hal. Hal's dad hugs his son, gives him a confident smile. Hal's father gets into his plane, ready for the show in front of the hundreds of onlookers, but disaster strikes, and the plane explodes as it's taking off. Young Hal horrified. Hector can't take his eyes away from the wreckage. Carol tries to comfort Hal. Cut to title sequence. [In the actual film, we don't discover about Hal's dad until a few scenes later. Having this at the beginning allows us, as the audience, to get grounded in a concrete reality we can recognize before we head off to spaceland. It also gives us emotional attachment to Hal Jordan and establishes relationships between Hal, Carol, and Hector from the beginning, unlike the film, which kept going back to let us know after the fact.]
After title sequence we see space, then a wasteland planet. Forbidden Zone flashes on the screen. 17 years later. Brief silence. Then a space ship appears, being chased by the monstrous Parallax. The ship crashes on the planet. An injured Abin Sur crawls out of the spaceship and has a fight with Parallax. Summons his power, seals Parallax in the planet. Abin Sur contacts Sinestro, saying Parallax is bound again, but Abin Sur is too injured. Must find replacement. Crawls back to ship, uses green energy to do some quick repairs, then punches in coordinates. The ship takes off. [Notice that this scene has Parallax being bound. The point here is that Parallax still injures Abin Sur, tainting him with the yellow power, which will then have the same effect on Hector later in the movie, but we only have to worry about one villain for this film, that being Hector.]
Hal wakes up, very groggy. He looks over at his alarm. Cursing, he gets up quickly and starts changing. [Notice I took out the one night stand girl? Completely unnecessary for the movie. Felt like it was only there to remind people that this was, in fact, still Ryan Reynolds.]
Hal is driving borderline dangerously, grabs a box from the passenger seat and starts, with one hand and his teeth, wrapping (poorly) a gift. He arrives at the airfield.
As he enters the dressing room, Carol Ferris lectures him on punctuality and responsibility, and how never takes his jobs seriously. He makes a snide comment about their past relationship. She says, "Well, you treat people like your jobs." And storms off.
Hector comes to see them off. Awkward. Hal, though somewhat condescending, still likes Hector. As they leave to run their tests for Ferris Aircrafts (run by Carol's father) Hal chides her about Hector having a crush on her. She shushes him with annoyance. [In the film, there was none of this development. Kind of necessary if you want the movie to have any emotion.]
Hal and Carol fly against the new aircraft. Hal does crazy things to win. Get's aggressive. Remembers father. Freezes up. Basically the same as the actual film. Afterward, Hal gets a lecture. Suspended. Carol tries to console him. After her previous lecturing, she's softened for him now, even as he denies that he froze up because of his late father.
Abin Sur's ship crash lands on a beach. He whispers to the ring to find the next lantern. Green energy leaves the ring and takes off into the sky.
Hal arrives at his brother's house, where a bunch of kids are clearly having a birthday party. Hal doesn't see the specific kid he's looking for. He enters the house and talks to his brother. Brother says his son, Hal's nephew is upstairs. They are all watching news story about Hal's accident on the test run today. Goes up stairs and talks to nephew. Consoles him and gives gift. [This is in the movie. And it was good. It was the only real emotional connection made in the movie. And you never see this family again. What?! I'll change that.]
On his way home, now night time, Hal sees green energy. Pulls over. It masses around him and he's whisked away to the crash site. He sees the crashed spaceship, runs over to find Abin Sur. Abin Sur gives him the ring and the lantern. Hal Jordan has to flee because helicopters appear. Panicked, he goes home.
Military and obvious secret type people show up at the crash site. They are taking the body of Abin Sur and investigating the ship. Carol's father arrives. Military guy asks if Mr. Ferris has people to work on the ship. Mr. Ferris says he also has the perfect candidate for work on the alien body. [This is to tidy up the unnecessary and extraneous characters that were in the movie.]
Hal is staring at the lantern and the ring, confused as to what to do. He puts the ring on and tries several things until suddenly he's basically possessed and starts reciting the oath. He's enveloped in green energy and then vanishes. [This is happening earlier than in the actual film.]
Hector is driven to a facility where he is told he can't talk about this. Gets to see Abin Sur's body.
Hal finds himself, after being pulled through space and a wormhole, wearing the Green Lantern suit on Oa. Hal is introduced to all of the Lanterns, including Sinestro, who hates Hal.
Hector performs the autopsy. Gets infected with the yellow energy lingering in Abin Sur's wound.
Hal begins training. Montage of getting his butt kicked and failing at training.
Hector at home, in bed. In agony. He sees flashes of civilizations from other words getting destroyed by Parallax. Can hear the voice of Parallax in his mind.
Hal gets back story of the Lanterns as he's trained more. Learns of the different colors and what they represent. Learns the back story of Parallax.
Hector is teaching a class. Can hear many of the students' thoughts. Basically the scene in the movie. He leaves. Can't think of anyone to talk to. Decides to head to Hal's house.
There's a knock on Hal's front door. It's Carol. Trying to find him. No answer. Hector shows up. Have a conversation. He can hear her pitying thoughts. He gets angry, but controls it. Starts to scheme.
Hal facing big test. Fails. Sinestro is angry with him. Tells Hal that he must learn to dominate his fear, to control it, as Lanterns must be without fear. Tells Hal that in his own homeworld, the people have learned to live through fear, having experienced tough times. Someone appears and tells Sinestro there is an emergency. Sinestro smiles and tells him to put Hal Jordan on it. Give the rookie a chance to prove himself.
Hal and another group of Lanterns go out and rescue an alien vessel that was floating derelict. It turns out to be an ambush by Zamarons [for the Green Lantern fans] where Hal Jordan ends up saving everyone. Earns the respect of the other Lanterns, but Sinestro still doesn't like him.
Carol is very worried about Hal still being gone. Family is concerned. Hector tries to keep Carol company. Gets bursts of her thoughts to figure her out. Uses this knowledge to try and lure her in. On a "date." In the midst of it, Hector begins having pain. Can't focus. Carol is still thinking about Hal. Hector gets angry. Then pain gets too intense. Hector's skull starts to swell. Carol offers to take Hector to the hospital, but he makes her leave the house. Gets more Parallax voice. Telling him to infiltrate the DEO and get Abin Sur's ship so he can repair it.
Hal is told his first round of training is complete. He heads back to Earth. He arrives at his house to find police, worried relatives, and tons of messages in his voice mail. Carol shows up. Tells everyone that he just needed some time to himself.
Hector gets into the lab, kills several guards (good time for a Wilhelm), and makes off with the ship, his telekinesis growing more powerful, but his head getting bigger (literally.) Military people give chase.
Carol and Hal are walking through the city, talking. She talks about how worried she was and how worried the entire family was. After their conversation, Hector, now trying to power the ship with his yellow energy, is fleeing military but destroying everything in sight. Hal sees this, tells Carol to go home. She refuses, but then he convinces her that he's right behind her. He, of course, slips away and goes Green Lantern mode.
Hal confronts Hector and they fight. Hector realizes, via powers, that it's Hal, and begins to flee, throwing civilians in his way. He says he must get the ship space ready and manages to get away. Hal can't find him. Carol runs back to the action, following the Lantern, realizes it's Hal.
At Hal's house, he communicates with the Sinestro, telling him the situation. Carol overhears. She storms in. Sort of argument. But she approves with a scene ending smile.
Hector is working on the ship. Voices telling him he must remain hidden, get the ship ready, and head back into space.
Hal goes back to Oa. Talks to Sinestro. Sinestro talks to the Guardians, stating that they are not powerful enough to stop Parallax if he gets loose, as Abin Sur was the only one who ever could. Sinestro wants to create yellow ring to fight fear with fear. Hal says he can find Hector. Guardians agree. Send Killowog and Tomar-Re to help.
The search begins. They eventually find Hector. Have a sequence where Hector is holding Hal's nephew hostage. Big fight ensues. Hal destroys the ship. But Hector is now using Hal's nephew as leverage to force Hal to take him to Parallax. So they leave.
They arrive at the planet keeping Parallax bound. Hector and Hal have big fight. Parallax almost freed, but Hal wins the day, and Hector is killed.
Hal goes back to Earth. Meets with Carol. They talk. Almost kiss, but hold off. [Seriously, save stuff for the sequel.]
Hal is meeting with other Lanterns and the Guardians on Oa. They are proud of him. Sinestro begrudgingly agrees. Guardians tell Sinestro there will be no need to construct a yellow ring.
Denouement. Sinestro is alone. He pulls out a yellow ring. Another Lantern enters the room. Reminds Sinestro rather forcefully that he was not to make the yellow ring after all. Sinestro tells him that he's had this ring for a long time. How else would his world have learned to live through fear. Puts the ring on. Kills other Lantern.
[This would have been my first draft synopsis. Is it perfect? No. None of these will be. They are first drafts. But it does several things the actual film did not. Number one, it consolidates several story threads so that there isn't so much jumping around. Number two, as this is an origins film that needs to focus necessarily on Hal Jordan, you can't get away with two villains if you're going to make them both important. The movie tried too hard to include too much. Parallax needed to be in a sequel. Hector needed to be the main villain.
In Batman Begins, Scarecrow was not the main villain, but he also wasn't given the attention Hector was. Scarecrow was a just a pawn, and what information is given, is given in quick scenes that don't take too much away from the main plot. Going to devote anymore time to a villain, you're going to need to give them a good payoff. Plus, Parallax and Sinestro both get to be bigger elements in the sequels.
Third, on the subject of Sinestro, we've given him reason to actually turn. That he was always a Yellow Lantern, in essence. It's not a random betrayal, like at the end of the film.
And there's my take on the Green Lantern.]