This would certainly benefit from a longer timeframe. Three days seems very short for a project that seems pretty ambitious. Currently my biggest gripe is that the game lacks feedback. In case of the big slow guys, I didn't know if my shots actually did anything to them. Similarly- there was no instant feedback on getting hit.
From the other hand- the animations and sound worked nicely!
My advice is- for projects of bigger scope try longer jams- I can see this game getting really nice in the course of two week, or a month long jam!
One more thing- unity has the option to make a web launched games. Those are played way more in jams like this!