Pretty good game....
But here are some suggestions if you decide to make a 2nd one. First off, see about making it some what of an rpg style, the guy gains levels and can upgrade some of his skills (i.e. rate of fire, speed of arrow, damage, etc.) Experience could be based on where you hit a monster and how many arrows you shoot. Another thing you can do is add a main health of the fire. That way you can let more than three monsters through, if you do this, the monsters would have to be doing different damage. This would help in the gain levels aspect because the player would have to choose which monster(s) to kill first. You could (like other players mentioned, add skills like triple shot etc etc.
Overall, fantastic game, music went well with it, the flow of the game was a little slow for me so I decided to just look at the background most of the time. Great artwork. I hope like heck you make a second one because this one was awesome to play. Great job, thanks for the game, hope to see more!