The strangest 3D Mario game in my opinion: simply the presence of voice acting or the fact that the entire game takes place in a single island makes Sunshine a very unique 3D Mario. Aside from the general weirdness it's a really fun game, until you start trying to complete it fully.
The 100% completion in Sunshine is simply frustrating, it highlights some level design choices that I struggle to understand even years after beating the game.
So I would only recommend the game if you're not going for the 100% completion as it made my experience considerably worse