Okay gameplay, lack of variety, excellent water mechanics, and moderately challenging describe the game well.
Gameplay (6.6 out of 10):
In the game, you start at an airport. I spent nearly 90 minutes trying to figure out what you were supposed to do with the ooze stuff. I'm used to having to jump on everything as with Super Mario World and others like it but that didn't work. I was frustrated and had to resort to a guide to find out what I was supposed to do. Once that was resolved, I could play the game through without much difficulty... except those stubborn block courses where Mario has to use his jumps to navigate complex courses. Normally I'd have 99 lives rather early in such games, but I had a hard enough time keeping the lives as a result of those stubborn block courses and I frequently went from 99 lives (from playing the Delfino Plaza area and exploiting a bug) to anywhere from 40 to 90. This difficulty comes from the fact that you lose FLUDD, and the ever-useful hover nozzle. It's just the beginning incident and the block courses that cause the gameplay rating to be a little low. Outside these, the only other thing is the hotel area as it's very difficult and frustrating at times once losing 18 lives as a result of the timer running out for finding 8 red coins when two of which were so hard to find. Overall, Mario has plenty of jumping abilities and with FLUDD and the various nozzles, there are many ways to get from point A to point B. The only thing that doesn't make any sense at all is that, if Mario loses his hat, he loses health. Like losing a hat hurts you.... The most annoying thing is that you cannot pause the game while in mid-air. If it's to counter the cheat of exitting the area to prevent losing a life, they could've at least just disabled the "exit area" option until landed rather than just disable pausing altogether. Super Mario Sunshine has a good camera system making it easy to control. It does have a big weak point, particularly with the area behind the ferris wheel and other tight areas. It makes things very difficult in these cases but since everything is mostly just open space, this isn't particularly problematic.
There are at least two bugs in the game that I know of. When Mario drops down into the sewers in Delfino Plaza and heads toward the bottom of the screen and bounces along the ground in short hops, Mario "drifts" a little off center of the screen and when he fully stops and goes in the other direction, the camera movement is rather awkward. The other bug involves falling from great heights. Normally, Mario would get injured, but in a swan dive and some other cases, he doesn't get hurt even though he may jump off of a 150-foot cliff onto solid ground.
Graphics (9.5 out of 10):
The first thing I noticed with the graphics of the game is how realistic the water is - it seems very life-like, a perfect 10 rating. Then of course, I haven't been to a beach by the ocean so I have no idea how it compares, but given medium-sized lakes, I'm very certain of it. The waves, however, seem rather large, much bigger than I'd expect to have seen. The graphics earn a high score as almost everything is quite life-like with a few rare exceptions. The lava is one such weak point as well as grass textures. You can see many of the various areas you visit in the game from nearly any area. For example, in Delfino Plaza, you can see Ricco Harbor and Pinna Park, and, at the right angle and position, Gelato Beach. The areas are all realistically and accurately spaced. Being used to the 2D Mario games, I was disappointed in the lack of variety. Everything is a tropical theme involving water at pretty much every point in the game. In the 2D games, there were forests, deserts, grasslands, lava-packed castles, dozens of pipes, the sky, and other themes. Super Mario Sunshine doesn't have this as there's very little variety.
Sound (7.3 out of 10):
The sound scores rather low due to the voices and the sound effects. Instead of actual voices, there's a lot of "yipee", "wahoo", "uh", "oomph", and other things instead and they occur a lot causing it to get rather annoying. The only time where voices are present is during the story cut scenes such as the intro flight. When speaking to the residents of the area, only text displays usually with a laugh or something preceeding it but no actual speech. This is the game's main weak point in terms of sound. The sound effects are much better than the voices, but still need some improvement. The sound effects seem more like that of the Genesis era's average.
The music is decent though, especially that of Delfino Plaza which has a very catchy tune. Past themes from the Mario games (such as when dropping into the sewers (which plays the theme of world 1-2 in the original Super Mario Brothers for the NES, but, of course, enhanced)) are present.
Value (8.6 out of 10):
There's a good 15 to 30 hours' play time in Super Mario Sunshine, but it takes much longer to find and obtain all the shine sprites and blue coins. There are very few self-made challenges that are available hindering the value.
Tilt (8.1 out of 10):
Super Mario Sunshine has a good story but the game itself doesn't seem that original. Sure it's unique in some ways, but the lack of variety really makes it difficult.
Other comments:
Using the "low gravity" cheat from Action Replay certainly adds a lot more challenge to the game but then again, when being able to jump very high, the swan dives get more entertaining. And yowsers (or is it Bowsers?) can Yoshi jump high with this code.