The atmospheric music was great! I loved the sprites you made as well. The controls felt a bit clunky, but that added a level of difficulty that made the game unique. Also - I love the way that the character keeps flipping when he's walking one way and shooting another way. It cracks me up.
Also I think it's pretty cool to have done this with your brother! I did my first game jam with mine. I did my game in a team too, and we got some sweet music as well. Take a look :)