Buy it
Gunstar Super Heroes pushes GBA to its limits. Both in graphics/animation and playability. It is a pretty short game if you want to see the end credits only. You can finish the easy difficulty in one go. There is a big replayability though, because of the 2 main characters to play and 3 difficulty levels, so don't worry about the lenght. Moreover the game is insanely intense and fun just to play, so you will back to it many times.
I spent 40$ for this game and I'm happy with what I got. Its worth it.
Rank: 5 out of 5.