As mentioned above,
Spongebob: Atlantis Squarepantis gives you control of Spongebob, Patrick, Mr. Krabs and Sandy as the four characters travel through the Lost City of Atlantis looking for long forgotten treasure. This adventure starts when Spongebob and Patrick discover parts of the Atlantis Amulet. This strange medallion will, according to legend, open up a pathway to Atlantis when it is put together. So when the two characters put the whole amulet together and a magic bus appears, they have to take it.
The story itself isn't all that bad and it has a definite Spongebob flair to it. In levels, you will have two characters available to you, the one you are currently controlling, and a second one you can switch to at any point. Each character has a different attack (Spongebob can blow bubbles, Patrick licks things, etc.), but besides that, they are pretty much all the same.
The game's levels are fairly straightforward. Like I said, this is your basic side-scroller. You will run through the level looking for various treasures (shells, golden spatulas and so on) to increase your experience and run across various enemies, like jellyfish, that can be attacked either by using your character's ability or just jumping on top of them.
Sprinkled about the game are mini-games like just before the Magic Bus arrives, Squidward attempts to teach Spongebob and Patrick music by having you tap (A), (B) or a D-pad button in time with notes that fly across the screen. Normally, this particular type of mini-game would give me trouble (being one of the timing-impaired and all), but I quickly found a flaw in this game that made it almost impossible not to pass. While most games of this sort make sure you press the desired button, and only that button, when the time is right, this mini-game just makes sure you are pushing the button they want. Consequently, I was able to push all of the buttons at the same time, and as long as I was somewhat close to the timing of the song, I got the points. The other mini-games provided in Spongebob: Atlantis Squarepantis aren't much better, but at least they did offer a little distraction from the game.
Now for the one thing that always irks me, passwords. Yes, instead of opting to save your progress, Spongebob: Atlantis Squarepantis uses passwords. Come on people, I don't care if this is a GBA title, we have long since passed the time when we need to use passwords to keep track of where we are in the game. It's always a hassle to get out a pen and write the password down, and to make matters worse, there doesn't seem to be a way to look up the last password you were given in case you have to put the game down unexpectedly. It wouldn't have been nearly as bad if I could have just looked up what the last one generated was, because then I could copy down the password whenever I felt like I needed to, instead of every time it came across the screen.