Had fun with this and i think you have a good foundation for a more complex game and room to implement more mechanics.
A few suggestions:
- I did like the level design and the use of the art assets however they could definitely do with a little cleaning up in some areas. Some of the wall textures were a little blurry and some still had their background colours which were noticeable.
- In terms of gameplay: For me the shotgun hit detection didn't work a majority of the time and the movement felt a little sluggish for my liking.
Keep it up, you're on to a good idea here. If you decide to flesh it out in future I'm sure it could be a great game.