Why willpower? Why not an actual emotion like courage? Well, emotions are volatile, and the more obvious choices have been shown to brainwash their Lantern users. Thus, the neutral power is a state of mind rather than an emotion.
The Green Lantern: Rise of the Manhunters video game, in its loading screen will occasionally show a message along the lines of "The Green Lantern Ring generates its bearer's costume, based upon physiology & culture", which just seems to be a note about every Lantern having a different costume. The Fridge Brilliance kicks in when you realize that there's a piece of free DLC available, which unlocks Hal's costume from the comics... or rather, unlocks a re-skin of his movie costume to resemble to one he wears in the comics. The ring is generating Hal's costume based upon if the player is more familiar with the comics or movie.
In the Film, Sinestro didn't steal the newly-forged Yellow Ring which Hal advised that no one should use... it broke out on its own and chose him.
In the comics, the normally dainty, delicate, and generally softening emotion of love is represented on the emotional spectrum by the Predator: a huge, intimidating, reptilian biped. Basically, it's a purple dinosaur that's all about love.
Parallax is, in science, essentially the difference of the perceived position of an object when viewed from different lines of sight. Now, why name the representative of fear after that? Because everyone sees fear differently.
Originally, the name was chosen because others perceived Hal as changing when he became a villain, when he believed the only thing that changed was his perspective. Fridge Logic set in almost immediately, with Hal himself frequently insisting both that he hadn't changed and that he had.
Let's not forget the compassion entity of the Indigo Tribe. Proselyte comes from proselytism, meaning conversion. What does the Indigo Tribe do? Brainwashing sociopaths into becoming empathic heroes. Aka convert them. Well done Geoff, well done.
Out of all the corps, the Star Sapphires stick out like sore thumbs, with their Stripperiffic outfits (while the other Corps have the standard Hard Light suits) and their tendency to only choose women. Why would this be the case? Well, considering their entity, the Predator, is a guy...
While the emotional spectrum has nothing to do with the chakra system, you can see some influences in the symbol designs. Both the Red Lantern Symbol and the Muladhara have four sections, both the Indigo Tribe symbol and the Ajna have two petal-like structures around a circle, et cetera.
Kyle Rayner is the butt of a lot of jokes because his mask makes him look like a crab. But it serves it's purpose quite well of hiding Kyle's identity, as opposed to Hal's much less ridiculous looking mask, which makes him look like...Hal Jordan...in a Domino mask.
With Lights Out over, it's readily apparent why the Guardians assigned only a single lantern to each sector; they knew of the possibility of the Dimming already, and refused to accelerate it.
Dex-Starr showed more intelligence than most Red Lanterns post-conversion, and certainly more control. It's possible Atrocitus boosted his intelligence the way he eventually did the other Red Lanterns, as Atrocitus clearly favors Dex-Starr.
Debatable. Blue Lanterns can heal wounds and making a new heart should be child's play compared to reducing the age of a dying star.
In that case, let's hope they can keep Atrocitus on life support the moment he gets out.
Turns out he survives for quite some time, albeit with a good deal of pain, and he eventually gets the ring back before he can drop. Dude must have been taking lessons from "Hey I can talk without lungs" Lordgenome.
That doesn't fit with, well, anything we see of Sinestro in the whole movie. This is a "novice" that he just said, in front of the rest of the Corps with a smile on his face, was a great guy. There is nothing, nothing at all in the whole movie, hinting that he might feel this way.
Because for all his Character Development, he's still an individual who thinks that with enough directed power you can overcome anything. And he's just seen what a powerful force fear can be... It's likely that in a Sinestro-based sequel or spin-off, he'd start off still relatively benevolent before taking a swan-dive into villainy.
Sinestro spent all movie believing that Fear was stronger than Will, and that it was essentially an untapped resource; he believes that Dark Is Not Evil and plans to use Fear to fight evil as a Well-Intentioned Extremist. He has witnessed his group of Green Lanterns (Will) being completely out-powered by Parallax (Fear) in a straight fight. Hal killed Parallax though trickery, not sheer strength.
Sinestro is also the mastermind behind the yellow ring, or at least the one who encouraged the Guardians into its creation. It was his project, and from his point of view it's perfect and the Guardians are holding him back, and will probably have no reason to deploy it at all with Parallax gone. So, in frustration against the restraint and perceived weakness of the Guardians, Sinestro resolves to go it alone and use what he has (directly or indirectly) created.
Perhaps Sinestro is also (more than) a little power-hungry, and as noted he sees Fear as more powerful than Will. He seems too eager to use the yellow ring, and ignore other options. He doesn't just want to see Parallax beaten, he wants to use the situation as an opportunity to "trade up" his ring.
A lot of Green Lantern villains have had this happen to them: Black Hand was recently outed as a necrophiliac, Hector Hammond is constantly trying to mindrape Hal Jordan in order to steal his memories of all of the sex he has had over the years whenever he's not having his powers jammed, the Manhunters committed an act of genocide against an entire space sector (Sector 666) that was then COVERED UP by the Guardians because they didn't want anyone to find out what their creations did (cause who would trust them to run a police force after their first police force did that) and the survivors (who were naturally pissed off at how everyone and everything they ever knew or loved was dead) were isolated to a lifeless world and left eternally crucified in terms of being made to suffer horribly so as to not give the Guardians bad publicity.
The Hector Hammond thing took on ultra-scary terms when you see him LITERALLY eating Hal's memories in Green Lantern (vol. 4) #62.
A sort of Meta-example, both of Briliance and Horror. The Blue Lantern Corps, and the Blue Rings of hope have so far been seen as the most benevolent Corps. When you look over at Warhammer Fantasy, the God of Hope is Tzeentch, a Lord of Chaos. Most of the Blue Lantern Corps individuals are religious and saintly, and hand-chosen by a member of the Corps. Considering that some folks are unfettered in attaining their hopes, this was a good idea, but what if a Blue ring chose someone unfettered...?
Never happen. As we got to see when Jordan visited the Blue Corps' home planet, Blues pick fellow Blue recruits, whereupon they're taken to the Blue Battery and interviewed by the two Guardians who started the Blue Lantern Corps. Ganthet and Sayd weren't taking any chances on a repeat of Sinestro or Laira's father.
Then again, sociopaths can hope, and in fictionland, they're such good manipulators...
It gets worse. The Third Army infects/assimilates by physical contact. The Green Lantern comics have established that sentient microbes exist. If one of those species gets converted, you might not know the Third Army is coming for you until they're already in your lungs.
Wait wait wait what? Hasn't anybody noticed that of all of the "emotions" on the Emotional Spectrum, only four of them are actual emotions? (Rage, love, hope, and fear). Will and avarice are just character traits, as is compassion, though the later-most can be induced or bolstered by empathy or sympathy.
I had always understood them as more motivations, than emotions. You would act out of rage, greed, fear, will, hope, compassion or love because they are what give you the strength to perform an action, just as the rings do.
Geoff Johns has stated that this is how he sees the colours of the emotional spectrum. They're not necessarily feelings per se, but they're all basic drives.
Heck, let's look at it from a different angle. Joy is an emotion, but in terms of motivation and "power", it'd be a terrible emotion to power a corps. After all, happiness is dependent on nothing going wrong, since the instant something bad happens to any degree the happiness of anyone is destroyed. It'd be like making a spear out of glass: technically it could do something, but it'd shatter so easily as to not be worth bothering with. At least Hope intrinsically has the quality of being able to exist in the face of adversity, even if it could be broken given the right leverage. Sadness would also count as an emotion with little motivating power, since it comes when spirits are lowest, and people only come out of sadness when it's substituted by a stronger feeling, like anger or will or love.
The emotions in the spectrum aren't actual emotions as much as they are feelings. Greed isn't exactly an emotion but it is a strong desire to own something for yourself. Being greedy isn't a deliberate choice someone makes, it is a feeling you can't control based on emotions like envy. Compassion works similarly, being based on empathy which isn't an emotion itself but instead is the sharing of emotions. And willpower isn't an emotion at all but that is the point. The Guardians rejected emotions and settled on the most stable band in the spectrum. The seven emotions in the spectrum are all tied to emotions in different ways and this is reflected in their powers. Straightforward emotions like love and fear have powers similar to the straightforward willpower. Hope, the passive emotion, is itself mostly passive. Compassion uses empathy to replicate other powers. It all makes sense if you view the "emotional spectrum" label as a matter of convenience.