I was born in 2002, and I remember playing on my Gameboy Advanced SP all the time!
Out of all the games I have fond memories of, Gunstar Super Heros was by far the most FLASHY, STYLISH AND GROOVY game.
While the original gunstar heros has multiplayer, more replayability and lots of fan far compared to Gunstar Super Heros, this game is more beautiful, and I believe the soundtrack to be one of the greatest on the GBA, if not of all retro games!