thanks for the feedback! I added more upgrade levels (Bow level 1, 2, 3 etc) to make the gold upgrades last longer.
I'll improve the enemy graphics and make them attack the player, sometime in the next few days.
Btw, this is a very early version of the game (I didn't actually expect people to play it so soon :D). I have plans to add more enemy types, upgrades, skills, weapons and some simple story.
Thanks again for playing and giving your feedback, hope you'll come back again.