Let's switch it around a bit.
Are there any stages introduced in Ultimate that you don't like? Why?
Personally I think Minecraft World is... Very underwhelming. With something as creatively open as Minecraft, the stage is very bland. And I don't mean simple, I mean bland. Cloud Sea of Alrest is simple, but it stands out in it's layout and it's fun to play on.
Honestly I just don't like that much most of Ultimate new stages. I agree with you on Minecraft world, it's just very boring and since the gimmick of Minecraft is how big the world is, this would have been the time to do a new stages similar to Temple or Palutena's temple with lots of different distinct areas like caves and cool mobs, but they pretty much did nothing aside from a few blocks that you can destroy.
A lot of people are bringing Moray towers and I 100% agree that it's bad. It's such a bad choice not only beause the layout is not fun, but it's not even a really good representation of Splatoon. Even if you're specifically looking at multiplayer stages, Urchin underpass is like THE one that everyone recognize and that was used in every Splatoon trailer.
Mishima dojo is another very underwhelming one. The gimmick is fine, but KoF stadium did it so much better. Having only Heihachi as a cameo is also very disappointing compared to other dlc stages.
Hollow abstion and Northern cave are really good looking, but aside from that there's pretty much no reason to play on them because the layout is too basic (it doesn't help that I don't like the KH music in Smash).
I also think they went a bit overboard with the cameos in some stage. Yeah kind of ironic when I just said that I wish Mishima dojo had more cameos, but the cameos on Cloud sea of Alrest just feels very awkward to me. I think it's because the stages is just so small and having the character doing nothing on the small house feels very unnatural compared to KoF stadium. The cameos in Garreg mach monastery looks very weird too, something with their models looks very off to me.