I like this! Would love an option for walk to be a toggle though. Personally I dislike holding movement modifier keys. Something like an option in the keybindings for a key to act as a walk toggle, or an option in the settings for press to walk or it to be a toggle.
The shotgun fire animation needs a little work. Could study the classics like the shotguns in Doom/Quake. More camera kickback would help I think. Sound needs to be a bit more bassy as well. Overall it really lacks the "punch" a good shotgun requires in a game like this.
But it's enjoyable. Will definitely pick this up when it's finished!