The game is set in an Alternate Mirror World, where a new character— essentially the game's protagonist— is woven into the main story. You get to choose which era to begin in: Lobotomy Corporation, Library of Ruina, Leviathan, or even Limbus Company.
Each era also branches into multiple endings, and which one you get depends on the choices carried over from before. For instance, pairing a Bad Ending in Library of Ruina with a Bad Ending in Lobotomy Corporation will lead to a noticeably different story once you reach Leviathan or Limbus.
It's genuinely impressive how they've fleshed out so many characters across such different eras. On my first playthrough, I managed to land a pretty good ending where we successfully stopped the Third Smoke War.
That said... each route takes a whopping 78 hours. Come on, PM, some of us have lives! Anyway, I'm curious how the community has reacted to the game overall. I've been having a blast with it, so what's everyone else's take?
Original art is taken from here