Interesting idea!
So I have absolutely no self-restraint, which got me wondering.
Is there some way you could tweak the core mechanics of your game to FORCE the use of only one hand at a time?
Not quite sure precisely what that would look like (maybe you have to hold down an numpad key with one hand or something), but I think it could be interesting to explore.
Firing the gun felt nice and juicy, which was good!
( I'll +1 Adrien's advice below as well, a gentler difficulty difficulty ramp would be nice! )