I always got the feeling that this game was seen as a classic. I never owned a Gamecube growing up, but I'm pretty sure I remember my friend having one and playing Sunshine a bit (although he was way more into Zelda and Smash).
Eventually I got round to playing Sunshine the other year when Nintendo released a triple pack on Switch. It was fun! I loved the aesthetic and interesting water spraying mechanics. However the other day I had a friend round and we were emulating the game, taking turns to beat levels. It struck us how frustrating the game was at points - especially those platforming levels in which you lose the FLUDD. You really notice how slippy and floaty Mario feels in this. In Mario 64 and Galaxy, the movement felt so precise in comparison and you knew exactly how the character would react to your inputs.
The levels too seem quite harsh at points. The Ricco Harbor level which introduces the rocket nozzle has frustratingly narrow platforms with constantly spawning wind enemies. My attempts to get back up to the top after falling off felt like cheating - i.e. lining up the rocket to land on different ledges rather than going all the way around the map again. I couldn't tell if that was what the developers intended.
Overall I do really love the game, but it feels like an awkward transition in the 3D Mario series. As if Nintendo were trying to innovate with new mechanics before they'd perfected the basic 3D platforming. Is it just me, or do others feel the same?
Yes you're right about having more time and better reflexes back then, but at the same time I feel like I pick up on cues and understand more what the developers intended for the player the older I've got. I remember playing the same levels over and over as a kid and eventually losing motivation to continue (this is somewhat balanced out by the fact that yes, I'd have more time, and also I didn't have as many games - so I had more incentive to keep playing one to completion). Whereas nowadays I've got more patience and I can work out 'oh I'm probably meant to go that way' based on my experience of playing lots of different games over the years. I've built up more of an intuition for these things.
That said, I'm not sure I could beat many NES games!