Idea is good. Needs a lot of testing and design features, also visual cues to indicate what's going on. I found myself using rapidfire against everyone, just because it lets me kill faster, no matter the distance or crit damage. I found no indication of what weapon to use against who, guns are the same (just different colors) and it shoot very similar.
Guns could have been minigun/laser/rocket/etc. with elemental damage ice/fire/electricity/etc. applied to defeat corresponding robot/bio/fire/armored/flying/etc. types of enemies.
There's a big potential. Anyway, great take on the theme!