Well, now we understand what happened to Hal Jordan's fashion sense back in GL #50 -- he was possessed by an alien entity named (by no coincidence whatsoever) Parallax. This has been one of the leading "save Hal" theories, although most folks espousing it have pointed back to Lord Malvolio. On the other hand, Alan Scott is looking in rough shape at the moment, so Malvolio may be in play before we're done here. (After all, they did share the same costume design.)
It seems that Parallax was the "yellow impurity" in the Main Power Battery back on Oa, which was "necessary" only in the sense that it kept Parallax -- the evil embodiment of fear -- a comatose prisoner for eons. Of course, you can't keep a bad guy down and when Sinestro was trapped in the Main Power Battery as well, guess who woke up? This would also help explain why Parallax picked on Hal Jordan to try to infect, since he was apparently taking cues from Sinestro. (We don't get to see old yellow ring until the last page of the book, so I'm guessing this piece of the explanation will be in issue four.)
Anyway, Parallax manages to start infecting Hal with fear and doubt, the effects of which we saw under Kevin Dooley's editorial thumb, including Hal going prematurely gray and being generally boring. He finally snaps when the Guardians tell him to report back to Oa for disciplinary action when he tries to restore Coast City. Kyle, interestingly, notes that he doesn't blame Hal for getting cheesed off under the circumstances. He also (serving as Geoff Johns', the writer's, voice) notes that using renegade GL Sinestro to fight renegade GL Hal Jordan was probably one of the stupidest ideas that the Guardians ever had.
Sinestro lost, Hal destroyed the Main Power Battery, and Parallax possessed him and has been riding him ever since, unknown to Hal. Apparently the Spectre knew -- or, at least, the Spirit of Vengeance component -- but hadn't bothered to actually tell Hal what was up all this time. (Don't you just hate these know-it-all cosmic entities?)
Meanwhile, Kyle (under instructions from Ganthet, the last surviving Guardian, has snagged Hal's body from the center of the sun) and has taken it off to the JLA moonbase, where he spills all of this to Green Arrow. The moonbase's a bit of a wreck, because Guy Gardner (now freed from his Vuldarian DNA) has come under Parallax's influence, acquired a power ring and trashed the place. Oh, and John is trashing the JLA at the old Ferris Aircraft site outside Coast City. And Kilowog has attacked Ganthet.
Why so many wacked out Green Lanterns? Well, it seems that it's fairly easy for Parallax to influence GLs who are without fear. And he's doing so.
Kyle, of course, doesn't have this problem. He doesn't much like feeling Parallax come after him mentally, but fear lets him fend off the painful attack.
Sort of explains Ganthet's "You'll do," doesn't it?
I've beaten up the plot a bit with this synopsis, probably more than it deserves. Johns has done a good job trying to pull together the irreconcilable results of previous years of bad writing and editing. He's pushing the cosmic reset switch, but he's doing it with as much style and grace as possible.