I think I'd be into Parallax way more if it wasn't a way to sideline the character and if we could still have Hal as the protagonist. Also, it was just badly executed. Hal goes from grieving the loss of Coast City to maniacally murdering Lanterns in the span of a few pages. And like j9ac9k said above, too often, he was portrayed as "crazy" and "power-hungry". Those are not traits I'd associate with Hal. In fact, even if Hal goes rogue, I don't think the man with the greatest willpower in the world would do so because he went "crazy"; he'd do so because he genuinely believed in what he was doing.