Nice! Really dig the 3d zombie - I was actually planning on doing something similar in my game so really happy to see it done here :)
The thing I think could be improved on is indicators for hit. Right now it's not super obvious that the boss was hit, and I feel like it's missing some 'juice'. I also wish the art style was a bit more cohesive - I love the 3d in 2d but it does look a touch out of place.
Overall the ideas in the game was pretty nifty and I think this can be expanded!