I really liked the art! I think it might have looked even better if the background had had some texturing or a different colour to really make the pencil-sprites pop.
I liked that there are different weapons with different damage values, but it seems that this is flat damage values that apply in the same way to all enemy types. Have you considered making each enemy-type more weak/resistant to some weapon types? I think it would add some variety and strategy to weapon-choice.