The direct sequel remembered as a dissapointment... eliminate your preconcieved notions! It's a great platformer anyway.
Everyone should (and if you don't I suggest you go look for it somewhere and play it. NOW.) since it's fantastic. Mario Sunshine, on the other hand, gets a bad rap for reasons I don't understand. What I believe is the cause of this misconception is that it doesn't really tinker too mucn with the 3D Mario formula. In fact, it is the same game with improved graphics and a couple extra moves, to be frank...and it takes place on a tropical island. The thing is, Mario's game really didn't need much tweaking to begin with, and what we get here is a refinement of that formula. The new game can get a little frustrating at times due to minor technical problems, but rest assured this game is a worthy entry into the Mario series.
So, what's new here? Mario get a jet pack powered by water named F.L.O.O.D. (Hardy har...I do enjoy name puns) with which he must "clean" Isle Delfino after being accused of messing up the place. Apparently a clone of Mario has been wrecking stuff up, and it's your job to stop them. Again, Mario games have never been strong on plot, and it's not like it has to be. The jet pack gives Mario some additional abilities; for instance, he can use it to float in the air for short periods of time, spray water at foes (which you'll be doing. Alot.), becoming a fountain, and use it as a rocket booster. All of these are used fairly well for each of the game's various Shines (basically, the equivalent of stars for Sunshine). All the various moves you know and love are still here, including the myriad jumping moves, the backflips, and the butt stomp.
However, it's not all fun and games. Mario controls really well most of the time, as the Gamecube Controller is perfectly suited to the game. However, even with the addition of the C-Stick, the camera can be a little wonky at times. It will not be enough to throw off your timing in most instances, but it can get fairly annoying in some spots (the theme park level comes to mind...). Also, the voice acting is a matter of taste. Some (like me) just saw it as an extension of SM64's actors. However, others can't handle the overt cutesy nature of the game. The graphic reflects this too, as the entire game is drenched in bright colors like a summer vacation. Sometimes the colors are a bit washed out (I believe it is supposed to be an effect of the sunlight). I personally enjoy that kind of style; it hearkens back to the days when gaming was all about fun. It's a break from GTA, to be sure, but it's still just as good.
Whatever the case, there's lots of stuff to do. You only have to gain about 50 Shines to get to the end (which seems a little small), but for the completists, there is plenty to do. Again, I believe there are about 120 Shines, and that's a whole lot of challenge. Each one of these shines is found in creative tasks - the boss fights being fun, but easy, highlights. If you don't like jumping, then stay away; many of the jumping challenges in this game are fairly difficult in comparison to SM64, but I personally loved the difficulty. It wasn't too hard, or too easy, and as long as you learn your entire arsenal of movements, you'll do fine. It does force you to learn the game, which is definitely something that should happen more often.
As for special stuff, I have to spoil this - Yoshi's in the game! Though it's not exactly unbelievable, it's still fun - he has fruit to spit instead of the water (a SMW 2 reference, I would suppose) but it's just fun having him in. I have to say that the final fight was...dissapointing. A classic villain reappears, but it's sorta a pushover in comparison. Still, it's enjoyable for what it is.
As is this game. Sunshine is worth playing - it combines the solid gameplay of the original and transfers it to a more graphically inclined system to create a wonderful, exciting experience. Though it may not have the unbelievable appeal of the first game, or anything that new, it doesn't really need it. Think of it as an extension on an old classic.