In retrospect, it's aged a little better than the initial reaction /co/ gave it, especially compared to the likes of true disgraces like SJ s5, SvtFOE s4, etc. But I wouldn't call it good. Better than most of the schlock being posted in here as better alternatives (middling CN comedy shows totted as watchable by the borderline shills here that crawled from the primordial ooze of Turner Broadcasting Studio's online PR department) but certainly not up to snuff with the rest of the series.
The main problem was that Bill was more of a Silver Surfer type character than Galactus. Something that was supposed to lead to something infinitely more deadly. Yet he ended up being the final boss regardless, despite having been beaten numerous times before often with risible ease. Bill's motives, origin, and exact nature were only really elaborated on in the cash-in "fan bible" books that happened after the series ended. Likewise, the apocalyptic event he was bringing just turned out to be a locally contained frat party with some weirdo creatures running around played by Alex Hirsch's crypto-pedophile/Weinsteinian liberal talkshow "comedian" friends and even Bill's scariest attack (turning people into gold) was rendered impotent by its pathetically short and unsustainable harming effect. In the end, Bill did less to harm the 3d dimension than Star inevitably did when she actually managed to merge two worlds together. A "trillion year old demon" got outdone by a horny teenager.
Other problems existed too. Gideon's halfassed redemption, Pacifica's unnecessary damnation, the lack of consequences for Stan lobotomizing himself, and the rush to the finish line. However, it's probably the best finale we've had for a real cartoon (not you, Over the Pretentious Wall) this decade.