If you're playing a Mario game for the plot or ending, anything short of an Alphadream or SquareEnix game and you're making a big mistake. I was just thinking earlier today how much vapid Peach agitated me. "I'm your momma?" she said, as if she ACTUALLY WASN'T SURE. I swear that was done as a knee-jerk reaction to her more confident appearance in SSBM.
I enjoyed a good deal of Sunshine, but felt that the game wasn't designed to be GCN's big Mario title. It would've been so much better accepted as a late N64 release. At the very least, it touched up some of Mario 64's rougher control aspects (and no more punching, at least, back to more of an emphasis on stomping), the water effects and draw distance were impressive (if a little overboard, in some situations it would draw the enviroments, but not the objects, so it didn't always do you that much good), and FLUDD had some interesting gameplay aspects (hovering to save yourself after a bad jump was gold).
The camera went completely daft, though. What was worse that if it was solely a dumb camera, I could absolutely deal with that, but you'd get to a certain area or point and it'd start FIGHTING with you, insisting on some inane angles. Pachinko machine, hurrah.
Also, looking back at early media for the game is confusing, because many aspects looked more advanced in the initial media. By the end, things became very boxy and N64-y, while the early videos had at least a Dreamcast vibe. I'm not saying the graphics were N64 level (but many certainly weren't using the GCN to the fullest, and the framerate went from 60 at the tradeshows to cut to 30 at release, and they couldn't even hold it thanks to issues with the water and reflections), but the designs and styles echoed that same boxyness and blurriness. It was developed with the previous console's design concepts in mind.
It's by no means a bad game, I just wish it hadn't been "the" big Mario game for the GCN. Why are we down to just one anymore, anyway? Back on the NES we had three (four if you include both SMB2s), and on the SNES there was arguably 2 (depending on if you count YI as part of the same direct series). The PS2 received at least three of their big platformer licenses (Jak, R&C, and Sly). I think the reason Sunshine stung was that we had to "make do" with that as the big Mario platformer title on the Cube, and if platformer fans wanted more, they had to scrape together what they could from the Party games and SSBM, or pay more attention to other series.