I beat the final boss on my first run lol (hint: focus on 1 form of attack and get the damage upgrade for it, and just be as aggressive as possible)
A glitch I have found: If you knock the ninja boss out of the building very quickly, he won't come back and the game is softlocked. I also glued one of his henchmen to the ceiling with a glue gun and none of my attacks could reach him, including the gun, machine gun and minigun, which may be another softlock in a very tall room.