I think it's a good game. Shure, graphics could be improved, but this doesn't matter much to me.
After I found out, that I am able to doge the enemys by moving (ASWD or Arrow-Keys) this game wasnt that hard. Even the enemys arent that hard to beat. Maybe this could be harder if you give them a bit of a life (like if you stay longer than 60 sec, they need to be hit twice)
Some bugs or downers:
The shop needs a bit to long to accept my click (takes about 1/4 - 1/2 sec ... which isn't critical, but not good. You should get what you click immediately).
Another slow-motion (when you get hit by that orange ball) ... i don't know ... it looks like a stucking or sth. could be a bit more smooth.
Other than that: good game.