Odyssey is pretty fun, and I think much of the post game is worth it. I finished final final level, but I didn't get all the regular moons. The four I missed were kinda tedious: 100 jump ropes, 100 volleys, hardest bouncy race, and giant Bullet Bill chasing me without Cappy.
Balloon world is fun too, and probably the most fun way to get coins. Got enough coins to get most of the costumes, but didn't go for 999 moons (I think you need to get all the regular moons anyway to get whatever bonus this is).
"so is my word...It will not return to me empty, but will accomplish what I desire and achieve the purpose for which I sent it." - Isaiah 55:11