If you haven't figured it out, the later wall gun can mount to the ceiling, and the last one can attach to the floor. It can be devastating if placed correctly, and damn hilarious watching him zip around.
I don't see what all of the fuss is about this game. It is like a poorly made Castlevania. The frustrating part should be the insanely hard bosses not the insanely bad game mechanics. I am sure if I took the time to examine this game fully I could find some merit in playing it. I however am not going to wait around for it.
Only when starting a new campaign.