The idea is very good! Could use more of a tutorial though.
I figured water would keep anything physical that walks at bay, and fire would be effective against zombies and vampires, and the cross against vampires and ghosts, but there were many items I didn't recognize.
So, some more clarity, and a slower start (so you don't have to deal with several enemies in a few seconds while trying to learn the ropes) would benefit the game a lot. Oh, and the game's time scale seems to stay at 0 when you restart the game (the score didn't go up and enemies didn't spawn).