Hugh Lowry has sent in a cool beatem-up called Triple Triad:

Hiya - just sending in my game that I made for my final year uni project.
First game I've ever made, and I'm very pleased with how it turned out .
Apologies if the difficulty is a bit misjudged - I've been playing it daily
since last September, so it might be a bit tricky for newcomers.

The game contains good sound effects and music, and is quite playable

http://www.gbadev.org/