Mario Sunshine is one of those games that could have been done better, but is still very good anyway.
In this game, Mario, Peach, and the gang are all going to the tropical island, Isle Delfino, for a vacation. When they arrive, they find that the island has been polluted by a person that looks very much like Mario. Despite the fact that he just arrived, the villagers take Mario and blame him for the mess. Mario is then forced to clean up the mess that is left on the island, collect the Shine Sprites, the power source of the island, and save Peach while he's at it.
Gameplay consists of both jumping and using the new water pump on Mario's back, named Flood. Flood can be used to help keep Mario up over a long jump, help defeat enemies, and of course, clean up tons of gooey crap. This isn't a bad thing, but not a good either. Since Mario is limited to just a water pump on his back, you're limited on what moves you can actually do, and you become dependant on fresh supplies of water, which you must use to refill Flood. The camera can get annoying as well. It tends to stray at an angle, or directly in front of Mario. You'll get used to it in time, but it gets rather irritating when you're in a tight spot.
Sound is clear and done perfectly. Sound effects, such as splashes, Mario's shoes and many other things work perfectly. Voice acting is also done nicely. Yes, there is actually some voice acting in a Mario game.
Value is on the good side. You won't be done with the game too soon, and you'll come back just to jump around the large and beautiful environment. There are 120 Shine Sprites in all, so it'll take anyone a while to complete the game.
Overall, Mario Sunshine is one of those games that could have been done better in several ways, but is still a very good game anyway.