What fandom or community is the hardest to please?

My immediate answer - Sonic fans.

I don't really know what Sega and the Sonic Team can do anymore to make these fans happy. They've revisited the classic formula a few times, they tried going modern routes, they tried 2-D sprites in some entries, they try going full 3D and whatever. Nothing ever seems to be enough and that's even when they've tried listening to the fanbase a few times.

Nothing seems to matter, regardless. The fans will find something to be upset about with Sonic. Anything.