Want Music? Theres an upgrade for that!
Great game. I find it sort of ironic that you try to send a message that there is more to games then fancy upgrade systems and that a fun game isn't built entirely on upgrading crap when this game is fun just for that reason! Theres so much stuff to upgrade =D.
P.S. Hints for new players:
The laser upgrade stinks, I had all laser upgrades and could not finish wave 20 at all, don't get these.
Missile upgrade is good but you can finish wave 20 with just the basic gun upgraded as well.