I figured you wanted "semi-auto" weapons. It works really well for the pistols and the infantry rifle.
My best attempt to explain why I like the shotgun to have auto fire:
Usually, having to press the button to fire the gun should give you more control over it, but not always.
An example of a good weapon to have no auto fire is your 9mm pistol. The firing state is really short, so you can hammer the button to fire off several shots a second.
It makes sense to turn off auto fire, if you didn't, the gun would be as fast as the .45 MP.
An example of a weapon that would be bad with auto fire off is the Doom standard pistol. Its firing state is long, if that weapon was made without A_Refire, you'd have to time hitting the fire button with when the sprite stopped animating, in order to get as many shots out as possible (I did a lot with the shotgun).
For your shotgun, since there's a reload animation between every shot, you can't really fire at the exact moment you want to, so it doesn't give you more control over the gun.
I felt a lot more comfortable with it as an auto fire weapon, I don't mind loading a patch if you want to turn off auto-fire, though.

EDIT - nice work on the textures so far
EDIT2 - The monsters still infight, is that a bug?