Did you make all the assets yourself? Some of them are very elaborate. I feel like the goblins and the skeletons do not really fit the style, though.
And as mentioned in a comment below, I think you need to give the player a chance to be able to avoid getting hit.
Also, I came to the first boss by avoiding every single enemy by jumping over them. Because I did not want to lose life before the boss. It didn't help me against him, though.
Your credits were funny!