In 1994 in an attempt to recover their failing sales and stagnant image, DC Comics decided to do a grand experiment. Namely, they were going to get rid of almost every major character they had and replace them with newer, hipper characters bearing the same name. In some cases this was a huge success (Death of Superman) others it fell flat before it even got started (Wonder Woman in a coma). The one that probably caused the most outrage however was the fate of Hal Jordan, the Green Lantern. Instead of having him fall heroically to a new and fearsome villain like the other titles, Hal simply went batshit insane after his home city was turned into a smoking crater and proceeded to destroy the Green Lantern Corps and and his overseers the Guardians of the Universe in a misguided attempt to make things right. In doing so he became the villain Parallax and became a major villain in the DC Universe for a while until his somewhat redeeming death.
Fans were outraged at this, feeling that a man as staunchly moral as Hal Jordan would NEVER let himself fall so quickly into a homicidal rage, and to a certain extent I agree with this. That being said I agree with it because I don't think the build was good enough. Quite literally between two comic panels do we see Hal snap. No deep quandary, or exploration of his helplessness and own mortality. Nope. One second he's kinda mopey and the next he's off to kill him some blueskins!
And in the grand scheme of things, that was the problem with Emerald Twilight; it was way too short. Whereas Death of Superman and Knightfall took months and months and months to tell and explore the whole story, Emerald Twilight lasted 4 months. And whereas the aforementioned titles took a great deal of time showing the sudden mortality of two of the greatest heroes in the DC universe, ET was, like I said, 2 panels long in terms of character arc.
The one positive thing that came out of Emerald Twilight was Kyle Rayner, the new Green Lantern who became a huge success, effectively saving the franchise. He was idealistic, far more playful than the stern Hal, and younger so he could appeal to a younger audience. He also had a horrible introduction and had almost no characterization for waaay too long. In fact, in many ways Kyles development is based entirely on the fact that every girlfriend of his dies horribly. Nevertheless, I personally prefer Kyle to Hal.
Writing aside, I do want to say that I was happy with the decision to replace Hal Jordan. He was becoming stale as a character and the steady stream of weak writers had been unable to expand upon him pretty much at all. He'd basically become Superman-lite, with the same infallibility and moral certainty that leads to stagnation and loss of quality.
To be honest, I actually even liked the Parallax concept. Taking one of the moral compasses of the DC Universe and turning him into a twisted version of his former self is a great idea and can open up all kinds of interesting stories. On top of that, bringing in someone who is clearly not as powerful or skilled as said villain and making him the last line of defense against horrible catastrophe is the epitome of reluctant hero/underdog epics, which almost always draw in the readers.
Despite the fact that /I/ like the concept many people weren't so stoked and fanboy rage echoed across the internet and comic forums quaked at the thought of angry Hal fans charging through in their neverending quest to redeem Hal Jordan. DC stuck to their guns however, and wouldn't budge.
Until 2004 when they called Geoff Johns to shut up the fanboys once and for all.