I personally loved the random gunshots. It felt alive to me. Art was amazing and consistent. Only one thing, in the second world you have, I think, badly placed collider on the edge block.
The one thing that stood out for me was the main character. I don't know why but it felt really great, looked great and as I mentioned the gunshots felt amazing to me. Simple but alive.
On the other hand the background could use bit of work. With your pixel skills it should be easy.
Great work