the game itself is very enjoyable. easy to pick up and play and the rampant increase of enemys provided a decent challenge without over running them with difficulty which is pretty hard to do in a game like this. and of course there can always be improvements.
1. adding skills to the enemies are fine but why not allow the player skills as well? if you think about a game like diablo 2 with the rouge class there is a huge array of skills for archery. exploding, fire, freeze, multi, homing, pierce, ect. allowing the archer to get better through skills rather then just bows would help.
2. the damage system is a bit vague. double and triple for bow and arrow? does this mean they multiply on eachother so they do 6? or do they add and do five? now while its not to important at the beggining its gets much more so when you have double (stat increasing) triple and quintuple. this can do 10 or it can do 30 based on the actual system of adding. i think doing like dungeons and dragons and saying like +5 is a better way to go.
3. if you could add a bit more variety to the character and possible customization options it would make the game have more replay value. as it is once you beat it its pretty much done. like maybe a warroir who can be built like a tank or very quick so hes never hit. that kinda thing.
thats about all i can think of atm and im not sure if you will actually get to it. ill be happy to help if your interested in more ideas