I must say, I really enjoyed the visuals. This is really stylized and it makes me happy to see. The game is charming and fairly fun to play.
Recommendations:
The gun switching mechanic should be taking the front stage. This is your core mechanic; this is what differentiates your game from others and you should focus on it. Reduce the screen shake, add a VERY noticeable visual for your weapon changes. Create a ~semi~ unique way that each weapon affects your surroundings (enemies). Examples: Flamethrower leaves fire on the ground, anyone (including yourself) that walks through it takes damage.
Great job and best of luck!