A roommate and I beat Super Mario Sunshine together, getting 120 stars. We had a lot of fun doing it because we simply tossed the controller to the other when we got frustrated and sticked with the stages/worlds we enjoyed. (Retro platforming for me.) The only major problem we had was with the clean-up stages because we didn't look in the manual until after many tries to find the superior spray attack.

IMO, the main strength of Sunshine has over Galaxy which has been brought up before in this thread but seems to have dropped from the conversation is that it had a more open level design than Galaxy has. Which one you prefer probably comes down to preference, (open versus linear) but I definitely prefer open.

I personally enjoy figuring out where to go as it makes me feel much more satisfaction and achievement when I actually end up in the right place. Many more times in an open game I think "hmm maybe I can do this?" and have the joy of suprising myself if it works, and if it doesn't I just shrug and try the next my next idea. Although the hidden stars try to give you bit of this experience you don't get it that often in SMG since nearly half the Hidden stars are just feed a Luma to open up an alternate path and where the game does reward you for finding some hidden nook the positive feedback you often get is much lower than when you just complete the linear levels as frequently all you receive for doing something awesome or difficult is just a a 1-up mushroom, which won't even save after you turn the power-off : (.

Nonetheless, for the reasons everyone else has stated, I think SMG is a better platformer than SMS is an adventure-platforming game. I just wish there had been more free-roaming and discovery in SMG.

/Edit: People also haven't brought up that Super Mario Sunshine brought the best Mario series power-up into 3-D -- Yoshi. =D