There's some cool stuff in here. At first I kind of rolled my eyes a little bit at "use the blue weapon on the blue" etc. rule, but then when I saw that we were upgrading each weapon independently it felt like a more interesting idea. I appreciate that when you get to the minigun the little moment of spinup makes the weapon a little harder to use.
I'm not sure we needed the player to be one-shot-kill for the game to work.
I think the mechanic of needing to prioritize one enemy type to upgrade the "lagging behind" weapon was personally more interesting than "you can't shoot blue with red or vise versa" [which would also be harder to justify in a larger game too; it makes sense quite quickly mechanically but it would be hard to tie into a theme/backstory beyond colour coding... this is why elemental stuff is often easier to do in fantasy than SF, I think]