I'm digging the aesthetic and gameplay a lot here. Great approximation of the two games I think it's based on.
A couple thoughts: It could use a more clear objective once the game level actually starts, as I wasn't sure who to shoot exactly. Which I think is the point, but might need to be stated more clearly. Also, giving the guns a little more impactful sounds and the shotgun more power would have made it seem more important to grab different weapons and more satisfying to shoot.
Overall, great job!