"I'll let you comfort the pigs later." - Ok, we know what 'god' is into.
@Seregossa I agree about respecting this author for ending it when the jokes got stale (wish that happened more), but I would have been happier with a narration box of: "The End. Some say she's still trying to get the monster to eat her...", instead of the "god's evil and killed all the humans years ago, but some of them turned into demons" plot that's been cropping up repeatedly and is getting used to close things out. The premise of different JRPG-style fantasy archetypes (monsters, angels, elves, sacrifices, etc.) acting entirely opposite their normal depictions, while poking fun at cooking manga and serving up an elf in deshabille was fun. Turning that into this plot for an ending arc rubs me the wrong way.
One Piece mostly gets away with its immortality because, although its plot structures are repetitive and predictable, it's mostly an adventure story about traveling between new strange places and meeting weird people. It's a picaresque-ish story, not a long hero's journey kinda thing. It doesn't really matter that the basic plot beats of each island's arc are mostly similar, as long as the island and the people on it are interesting. Gintama is very similar, because as long as it manages to pull enough ridiculous parodies out of its capacious ass, it's still going to be entertaining as a set of loosely-connected interludes, rather than feeling like, for instance, Bleach, where Tite Kubo eventually just kept scrabbling to find things to lengthen the story.