Here's my angle on the subject. This is coming from someone who hates the 3D Zeldas.
Mario 64 was at fun because it at least focused more on the fundamental aspects of Mario and what makes it fun. Running, jumping, beating the koopas, etc, yay! The puzzle/exploration elements in a sense just served as a structure to tie everything together and to make better use of the small yet sprawling type of level design.
Mario Sunshine on the other hand makes at least two very sad mistakes. 1) it becomes even more convoluted with the puzzle element as well as gimmicks and this aspect takes over the game.... you have to find nozzles, you have to unlock Yoshi, you have to push a watermelon on a bridge, find coins of eighty different colors, find the door in the haunted hotel, you have to ride a rollercoaster on-rails shooter (that was purely awkward) clean up paint here and there etc etc. Less fun, more shit you have to do. And the other mistake: 2) Less running, jumping, and good fun Mario stuff. You now have fludd, which ruins EVERYTHING. Instead of jumping on enemies in 3D, which is true fun, you are now stopping and holding the trigger and aiming in place. OH MY GOD. And platforming isn't fun anymore either because now it's all about the nozzle, and Hovering for a Short Time, instead of natural platforming physics and skill.
In short Mario Sunshine does everything better on paper but at the expense of gameplay and fun factor. (kind of like every Nintendo game nowadays) >______>
It does look good.... however, it takes place in wherever it does, which is a washed out, ugly, repetitive tropical island/resort, as opposed to "Mario world". (Curiosity about this new locale rapidly wears off, since if you've seen one area it seems you've seen them all.) Also one particular complaint of mine is the whole deal that the lack of shines make the island dark... so you have a plaza in broad daylight, yet it is dimmed... so that's just kind of confusing.