Interesting game. A few criticisms. While playing I found the camera was too high so when I jumped I couldn't see below me which made dodging enemy fire a bit difficult. The health system could be a bit more prominent as most of the time I wasn't paying attention to my health as it was so out of the way. And lastly I wasn't quite sure what the general objective was I killed a big ghost and was put to the start. Some dialogue would help paint a better idea of the mechanics and story I think.
Other then that its got some good ideas.