The way you navigate your way from the menu to the actual game is very easy to do and has a bit of Mario flare to it. Instead of selecting which file you want to play on a list format, you play as Mario and hit one of three boxes (each one of the boxes contains a seperate play file). It's slightly creative and easy to do.
The opening cutscene, plot development, and overall plot are not bad either. The game has you, Princess Peach, and Toadworth start out on a plane to the tropical Island of Isle Delfino. When you arrive, you find that the sun is not shining quite as brightly and there is a huge puddle of goop right in the middle of the runway. A monster pops out of it, you kill it, and then you get blamed for making the mess, when, in reality, you are just being framed. The punishment you receive for "your" crimes, is to clean up all the rest of the slime that has been painted on Isle Delfino.
The visuals are colorful, the edges of the characters are smooth (but the characters themselves are a little blurry), most of the environments are nice looking, the animation is great and the particle effects are fairly believable. Overall, it is a very nice looking Gamecube game.
The sound effects are generally not very realistic, but this is a Mario game. One of the things that defines Mario games is weird sound effects. I don't think that they took much time into making good music though, seeing as I can't remember most of the songs. The only time there was any voice acting was in the cutscenes, which is typical for Mario titles but it definitely pulls away realism from the game.
I never get tired of playing this game. It's gameplay is the definition of fun. You get all of the high jumps and butt slams that you're used to seeing in a Mario game, but this time you have FLUDD, a cleaning device invented by Professor E. Gadd. FLUDD will help you by giving advice, killing enemies and clearing obstacles (depending on what nozzle you have at the moment).
You have to collect a certain amount of Shine Sprites to move the game along, but there are plenty of other ones to gather. You get some by completing levels, others by doing minigames, or you can purchase them with blue coins. It is definitely worth coming back to for seconds.
If you're a Gamecube owner, you should buy this game. It is one of the most fun games on the console. Good story, good graphics, decent sound and excellent gameplay are what make this game a fun, energetic experience for all ages. Stop taking my word for it and try this game out for yourself.