Super Mario Sunshine is a game I really love, I can come back and play this game any day of the week and I'll love it to pieces.
This game is the best controlling 3D Mario easily just moving around feels great for how tight and fluid it is, and using mechanics like the Spin Jump feels even better, FLUDD I love for its different uses, Hovering to save myself from a bottomless pit if I ever mess up, or launch myself high into the sky to maybe find something cool. Even that aside, doing things like Spraying Water, then diving, and gaining a ton of speed is a blast.
I also love the Level Design of this game. With exploring the sandbox like level design. The Secret Stages are also great with more linear platforming than the normal stages and offer a decent challenge, which feels like a breath of fresh air. While there's plenty I love about this game, it also has some lows. Some of my biggest problems with this game is simply how janky this game can be, and also some of the Missions in this game are just plain bad. The 2 most infamous examples being Pachinko Machine and the Poison River, the latter of which I find to be worse, not only is playing that Mission a pain, getting there takes far longer than it has any right to be whatsoever.
Also, the Structure of the game forcing you to play the Shadow Mario Missions for every level is pretty repetitive as well. However, something I do like about Mario Sunshine's Structure, is that every Mission has at least some difference in layout, unlike Mario 64 say, since it feels like you're going through different parts of the level or you're going through a level that's evolving. Overall, while this game is flawed, I like it a lot, and would definitely recommend you try out this game if you haven't already.