Impressive that you two made the whole game from scratch - I did the same thing and it was no easy feat. The only thing that would have been cooler than jamming out to heavy metal while shredding zombies would have been jamming out to heavy metal while shredding through zombies with sound. The music got me hyped at first, but the lack of feedback made it feel kind of incomplete. I'm assuming that was a time issue, given that you obviously had to spend a lot of time making your own assets. Believe me, I've been there. :/
Still a fun game nonetheless (even though I got an F).