I've completed the entirety of Bowser's Fury. Took me about... 8 hours or so (split across two days). It wasn't as long as I had hoped, though the content that was there was really fun. Obviously i wasn't expecting Nintendo to come out with a game the size of, say, Super Mario Odyssey, and hey, atleast we got the mode at all - Nintendo weren't obliged to make it, and they could have just ported SM3DW on it's own, so i'm really glad it even exists.
One gripe i had with the game was that each island / subarea basically all had the same goals - get to the lighthouse, get 5 shine shards, let fury bowser break a set of blocks... it felt a little bit repetitive (emphasis on the little), though each of these islands had a unique theme so it wasn't like you were replaying the same set of challenges throughout. The only other *super minor* issue I had was that to unlock new challenges in an area, you would have to collect a shine from somewhere else (fair enough though, since the areas actually update between main missions - I really liked that!). It only meant the missions didn't flow as smoothly as other 3d games in the series (in most games you can generally hop straight into the next mission of an area after completing the previous one).
Anyway, I really don't want to highlight issues, because frankly these were minor nitpicks more than issues. Overall I really enjoyed Bowser's Fury. Honestly better than i was expecting, Nintendo did a great job with this!
I'll be starting SM3DW tomorrow. Not expecting any new content (which is fine, since Bowser's Fury is the new content) but it'll still be fun to play through again!