It's amazing how much fun you can have playing games about things you don't have the slightest interest in or ever plan to do. Tony Hawk's Pro Skater implements the power of the GBA better than almost any other game. The controls are perfect, and 3D adds a whole dimension a Game Boy game, literally.
The features of the game are limitless if somewhat repetitive. You would have to spend upwards of a thousand hours to unlock all of the skaters and boards. This game proved that you could fit all the features of a full-fledged console game into a 2 3/8" x 1 1/2"x 1/4" cartridge.