I like the visuals you've got there, and the concept is pretty neat. However I think the mechanics as they stand are a bit unclear. As far as I can tell you've got limited ammo/ 'clip size' and need to reload every so often. But this can only be done when you've used up all of your current ammo, meaning you are sometimes caught short if you've not reloaded recently enough. Also though I've no problem with the unicorn itself, it is unclear where it's hit region should be. Presumably this would be around it's legs due to the perspective choice, but it's not obvious just by looking. I would also suggest making the enemy bullets slower as it's hard to judge if you're going to get hit or not when trying to position yourself.
I also noticed some sorting issues related to the unicorn being drawn underneath soldiers who were clearly supposed to be further in the background.
Anyways it's a cool concept and like I said before I think the art is really nice, and there's some good special effects in there. Also the music is good. Just think the main gameplay mechanics could do with tightening up and explaining a bit more clearly. Regardless this is certainly good for a first release.