Nice Game
I found this game to be really quite solid in practically every area. The gameplay is easy to get used to and very responsive. This, coupled with a fairly deep upgrading system made it a game one can get into and play to the end without losing interest.
I am really impressed by how much effort was put into not only bow/arrow/armor upgrades, but also the slew of enemies you encounter throughout the waves. The character designs are very cool and diverse. On the topic of graphics, the background art on the menu screens is very cool, I thought I'd comment on that, too. :P
If I do have any criticisms with this game, it's with the difficulty, especially during the boss battles.
Though there were subtle differences, the strategy against nearly every boss was the same: avoid the shockwaves and shoot. This got quite repetitive after a while. I would suggest adding unique methods of attack for each boss, and maybe weak points that are exposed at certain points of the fight to make things more challenging.
Another idea I had when playing was to have multiple locations throughout the game that the main character travels to after each wave. He could stop at villages/towns to upgrade/buy weapons and stuff. It's just an idea I was tossing around, I think it would give this game a much more adventurous feel and totally get rid of the repetitiveness of playing in the same location every wave.
Overall, a nice game, I really enjoyed playing. Nice work, and I'm looking forward the sequel!