Nintendo pulled a bit of a fast one on us.
I really really hate to be the bringer of bad news but oh well. After reading through Euro-Asia Game Boy's review on the Game Boy Advance I stumbled upon this paragraph.
Using the link cable extends the power of the AGB by allowing multi-player gaming. With 3 cables and 1 game cartridge, up to 4 players can engage simultaneously in a game. This is called, "One Cartridge Play". Unfortunately, there isn't many games that will support "One Cartridge Play" because of the limited amount of data that can be transferred from one cartridge. For example, in F-Zero, you can only play one course of the game (there are more than 15 courses in the full game) with "One Cartridge Play". Full multi-players games can only be realised when using 4 of the same game.
I think that pretty much speaks for itself. The Game Boy Advance's One Cartrige Play is a bit of a sham, in F-Zero Maximum Velocity at least. Other games might have more than 1 level playable.