It feels stunlock-y; getting hit knocks you around and stops you firing, making you unable to stop the enemy from firing, if that makes sense? Even if you're not taking damage with every hit you lose a lot of control of your character.
...Honestly I never actually noticed you move differently with different weapons. Maybe that could have been made clearer? Heck, if the pistol-mode could double-jump that would encourage its use a lot. Though given you shoot horizontal projectiles you still need to be level at some point with the enemy to shoot them, which jumping around a lot hampers. Currently, the best 'strategy' to use against enemies is to just stand outside their range and plink them. You'd need to either break up the long sightlines in the level geometry or make aiming free-directional to try and combat that.
EDIT: Oh, and despite the screen telling you to use a gamepad... you cannot navigate the menu with a gamepad. Or at least I couldn't with an xbox controller in Opera.