This is the idea I posted in the other thread.
Considering the film that's been made there's many potential reasons why  it didn't succeed. Too much fitted into too little. Maybe DC  interfering too much? Maybe WB interfering too much? Who knows.
They can still save this plane crash of a franchise by potentially   ignoring the **** that's gone down in this film and do a sequel with a  more emotional storyline.
Get rid of what they've done here and go for a more steely approach to   the story and make it a proper character based film without just being a   mindless action adventure.
Personally I'd love to see a film book-ended with the setup towards Kyle  being the last surviving member of the Corps who then faces off against  the ultimate villain.
THE PREMISE
Start the film off almost in a similar manner to how Abin Sur comes to  Earth looking to find his replacement but instead with Ganthet arriving  on Earth which is being rebuilt following what seems to have been an  extinction level event and him seeking out a ring slinger.
Through a little bit of exposition when he finds Kyle Rayner, the new  Lantern, we find out that a destructive force has almost wiped out the  Green Lantern Corps (no naming what it is) and Ganthet is looking for  Rayner to be his first new Lantern.
I'd do away with the fear-entity ******** Johns created to justify Hal's   actions and show Hal's descent to madness in a very real fashion   through the use of flashbacks charting the destruction of not just Coast   City but most of the the planet leading to a semi-post apocalyptic   world. 
Rayner obviously has questions, questions which lead into the bulk of  the film's plot through the primary portion of the film being a  flashback.
FLASHBACK BITS.
The film's plot as such kicks off with a pitched battle between the  Sinestro Corps and Green Lantern Corps on OA which results in both sides  suffering heavy losses and the GLC ultimately scraping through thanks  to Hal rallying his troops and turning over the Sinestro Corps.
We find out that Sinestro had turned against the Corps as a pre-emptive  strike prior to them reacting to his own dictatorial rule over Korugar  by stripping him of his ring by him harnessing the yellow energy of fear  to rise up against them.
This battle needs to be fairly short but intense depicting the polar  opposites of Hal & Sinestro with a little bit of exposition to  explain the above and the battle stressing the rivalry between the two.
Following the battle being won by the GLC, maybe a few shots switching  between Earth and OA would be good, showing the parallels of chaos on  Earth and order on OA but also showing some weaker moments of Hal with  his loneliness coming through but being comforted by the softer scenes  he'd share with Carol who is more than love interest but a proper  companion to Hal. Hal however needs to be seen in these moments to  question Sinestro's actions as well to try and understand what happened.
The main thing that needs to be achieved at this point is why Sinestro's  really fighting the Corps. Him having differing views isn't enough  grounds for him to just wage war against them, and neither is his  expulsion, even though it's seen as enough by many. Ideally it needs to  be down to him wanting control. 
Not just him wanting power but him wanting the power to control how the  universe is run and not in the soft manner the guardians want to run the  universe in. He doesn't want to stand by and watch whilst things go to  ****. He wants to play God on a big level and this needs to be his  motivation.
Whilst the GLC are celebrating their victory, or well not celebrating  but just recognizing their victory, and following some scenes covering  the ground of what's gone down we find that Sinestro's retreating forces  have already gone one step ahead of them and targeted Hal's home world  of Earth as revenge for their defeat.
The Sinestro Corps unleashes a nuclear equivalent attack on Earth by  focusing the energies of their rings through the Yellow Power Battery  almost destroying the entire planet resulting in the 2nd big throw down.
The destruction of Earth needs to be caused by Sinestro to prevent the  Cyborg thing coming into play with it being a revenge motive to show  that even the greatest Green Lantern (Hal) can be pushed over the edge  and how his control stretches to every facet of the Corps, even their  hearts and minds.
During the battle Hal goes out of control a little bit and you can see  him losing his battle with his own fear as he sees what Sinestro's done  to his home planet. They duke it out with Sinestro taking more of the  Corps down with Hal unleashing his power as well to take down all but  Sinestro from the Sinestro Corps with the GLC having to restrain Hal and  the Guardians intervening to imprison Sinestro in the Central Battery.
Even at this point during the battle you see Hal giving into the fear  emanating from Sinestro, and maybe you see the initial grey lines appear  around his sides just to lineup with the comics' aging style depicted  in the story-arc.
Hal surveys the wreckage of Earth and is taken away almost from a  comforting point by the remaining GLC to Oa to speak with the Guardians  about what's happened. 
After speaking to them he realizes that they're not going to execute  Sinestro but will instead merely keep him imprisoned in the power  battery, and he gets pretty enraged by this and also starts hearing  Sinestro's voice in his head as his conscience almost telling him about  the lack of control he has over the situation and how the Guardians are  almost not willing to wipe out the evil of the universe just so that  they have a job to do almost. Fear keeping the universe in line and all  that.
Hal flies back to Earth at this point but prior to him leaving you see  Sinestro in the Power Battery releasing the yellow energy into the  battery from his ring which was thought depowered by the Corps and  laughing to himself at what's happening outside.
Once Hal arrives on Earth he sees the chaos that's been caused by the  extinction level event brought about by Sinestro and starts questioning  himself even further about how inactive the Guardians are. You see his  good side come through as he helps a few people here and there on Coast  City but when he has an injured person question why he spends so much  time in the stars and not protecting Earth he kinda flips a bit and  seeing what he's becoming because of his inability to protect his home  he heads back to Oa to end Sinestro once and for all.
His justification for killing Sinestro needs to be that Sinestro is his  guilty conscience and also the personification of the weakness pervading  through the Corps. He also feels the Guardians fear Sinestro which is  why they won't kill him.
When he arrives on Oa to kill Sinestro he discovers the Guardians have  moved the Power Battery to a secret location as they knew Hal would come  for them. An argument between Hal and the Guardians ensues with Hal's  conscience clearly winning the battle in his own head throughout and  Parallax as such finally overtakes Hal.
He bursts out at the Guardians resulting in the 3rd action beat of the  film with him pretty much releasing all his powers on them and absorbs  their energy and begins to dismantle anyone who comes in his way,  Lantern or not and becomes Parallax. Not the gassy smokey version or the  fear entity, but just the badass that he was in the original arc.
With this battle you see that the only Guardian who supported him  Ganthet refuses to fight Hal but instead attempts to reason with him  whilst protecting the Corps.
He finally breaks through to Hal and contains him temporarily by  harnessing the powers of the dying Guardians and throws Hal into the  anti-matter universe with the bait of that being where Sinestro is. It's  depicted as a portal to another dimension without mentioning  Anti-Matter.
Ganthet bloody and bruised tends to the very few surviving Corps and  leaves a crumbling Oa which implodes behind him as he makes way for  Earth, thinking that he may find an emotional counterpart to Hal who may  save the Corps.
BACK TO THE FUTURE
We come back to the present where Killiwog and the remaining Corps, only  around 4-5 of them have been spread out to maintain order whilst Rayner  is recruited, who finds out that he was merely in the right place at  the right time and in anecdotal moment gets told that 'he'll do'. Rayner  asks for what and Ganthet replies 'for the Blackest Night'. This isn't  the Blackest Night of the comics but is the final faceoff between  Parallax and Sinestro.
In the present we find out that Parallax didn't find Sinestro and is  coming for the remaining Corps members who have settled on Earth to undo  the damage Sinestro did as he wants to extinguish anything that links  him to the damage he did to his home planet.
He arrives on Earth and an immense battle of will takes place between  Parallax and the remaining Corps including the newly knighted Kyle. 
During the battle we find out that Ganthet had housed Sinestro in a  pocket dimension and releases him following an agreement that Sinestro  would be given the control he desired as long as he helped chain Hal  down.
By this point Hal's gone so far over the edge that he's willing to use  his powers to destroy pretty much everything and start again. Naturally,  he must be stopped.
You have the final action beat of the film which is Sinestro, Killiwog,  Ganthet and Kyle versus Parallax but **** hits the fan when Sinestro  starts manipulating Hal for his own aims and further goads him into  doing what he set out to do. Sinestro assumes he can overpower Hal, get  him to destroy the Corps anyway and then prevent destruction resulting  in him being the saviour.
Problem is Hal/Parallax doesn't see it that way and plows through the  heroes and Sinestro anyway. He dismantles everyone including Rayner and  finally beats down Sinestro to an inch of his death whilst everything is  coming to an end around him. 
Beaten and bruised, Sinestro begins to laugh and also pretty much cry at  what he's achieved and says something along the line of him only  wanting to be the universe's saviour and protector and the Guardians  couldn't contend with that. At this point Hal's humanity creeps through  ever so slightly and he asks why and Sinestro responds 'so I can be in  control' and dies.
In a whole moment of his life flashing before his eyes, Hal regains  control of his senses and realizes what's happened. He goes for the Sun  which is the source of the hollowing he started himself and sacrifices  himself in the one final moment of heroism and prevents what he wanted  from coming to pass.
The film ends with Ganthet using a large reserve of his powers to help  rebuild Earth (Brainiac 13 technology style) and Rayner assisting this  process and the two of them flying into the darkness with new challenges  to face.
THEMES
The main thematic elements of the film in a similar way to any morality  tale would be heroism, sacrifice, the power that people desire and fear  of loss. There would need to be parallels of course. Again each of the  themes carry emotional weight and need to be balanced.
- Hal and Kyle are two of the same being. Hal shows his heroism in the  first and third act. Kyle shows his in the third and fourth act.
- Hal and Ganthet are willing to sacrifice. Hal is willing to sacrifice  his own life at the end of the film to save the universe from his own  actions. Ganthet, albeit stupidly is willing to sacrifice the entire  Corps to stop Parallax by releasing Sinestro, thus resulting in a bigger  storm.
- The Guardians and Sinestro both desire control. The Guardians want  things done their way which is their weakness, and ditto for Sinestro  who even when he dies does so satisfied albeit prematurely that he died  in control.
- Hal and Sinestro both have a fear of loss. Hal fears losing his mind  which he does. He fears losing his home, which he does through Sinestro  actions and loses his adopted home of Oa through his own power-fuelled  actions. Sinestro fears losing control and does everything to make  things dependent on him, even if that means risking the entire universe.
MAIN PLAYERS
Hal : He's the central part of the story with Sinestro. He is the tragic  hero ultimately. He is central to every thematic element above along  with Sinestro.
Sinestro : He needs to be evil, but again evil with a reason. Control.
Ganthet and the Guardians : The Guardians need to be like any orthodox  force. Old fashioned and stubborn, with only Ganthet seeing the errors  they made.
Kyle Rayner : The last of the Lanterns. He is the new student. He gets  his moment at the end of the film and hopefully in a sequel.
CONCLUSION
It's a pretty ambitious idea because ultimately if done wrong it could  be an absolute cluster**** but would be hopefully be pulled off by a  skilled team. 
It would likely be long. The film would be divided into five acts.
The Prologue would show Ganthet arriving on Earth to find Rayner who he  chooses as a Lantern and then explains to him what's gone down, and  dovetails into the First Act. 
The First act charts the battle between the Sinestro Corps and the Green  Lantern Corps. It also slows slightly into the emotional attachments  Hal has on Earth and his relationship with Sinestro. A second level  flashback would show the expulsion of Sinestro and forming of the  Sinestro Corps.
The Second Act would be the second battle between the Sinestro Corps and  the Green Lantern Corps; the destruction of Earth; and the imprisonment  of Sinestro into the Central Power Battery after the Guardians  intervene in the battle. At the end of this act you see the early  descent of Hal into darkness.
The Third Act would begin with Hal speaking to the Guardians about  Sinestro and their decision not to kill him; show the aftermath on Earth  with Hal's inner conflict taking place; the yellow energy being  released into the Central Power Battery and end with Hal's return to Oa  with his intention to kill Sinestro.
The Fourth Act begins with Hal confronting the Guardians; him learning  of their supposed betrayal of sparing Sinestro's life; Hal becoming  Parallax and taking down the entire Corps and destroying Oa; Ganthet  using his powers and the sacrifice of his fellow Guardians to throw  Parallax into the anti-matter universe with the bait of him facing  Sinestro there; Ganthet makes his way to Earth; finds Kyle and the film  basically meets up with where the prologue dove in.
 
The Fifth Act is basically the final battle as explained above in  detail. Everything goes down and all the loose ends are tied up with the  heroes being the heroes and the villains being the villains, but albeit  with the lines between the two very very thin.
The epilogue is the aftermath of it all. A new Corps needs to be built  with a new Lantern and a setup for the future with Kyle as the main man.
Opinions?