This has a good base for a game. I think collecting skulls should've been explained in the game itself as it took me a good time to figure out that I was supposed to be collecting skulls at all. Also after I got hit once somehow I couldn't collect skulls anymore. That should be explained as well I think.
As for the mechanics, I think the way you've set it up really encourages click spamming, and my finger felt really sore after a while :S
The music was really good despite being kind of drowned out my sound effects of enemies dying (which were pretty hilarious btw).