The chiptune was interesting, and pretty cool. I think it would be better if the lead melody wasn't looping constantly, because I can see it getting annoying after a while (assuming the zombies are being held off for extensive amounts of time). I suppose if this wasn't something you wanted to do, you could change the sample for that lead sound to something that doesn't sustain as long, like a glockenspiel type sound?
The only thing I could suggests for the orchestral piece was that the lower range woodwind (I think) instrument sounded a little too much like a sample instrument, so maybe try some chorus, reverb, or edit each notes velocity to make it sound a little more human; by the time the arpeggiated part kicked in I really loved the track. I think it's really good and quite pleasant to listen to, so it'd be well suited to a game.
All in all, I dig