A very nice stylized game, I know you've said this was a project for a degree program and as a fellow student doing the same I thought i might leave some feedback for improvement nothing crazy but just ideas to sit and think over
1. For the menu options everything doesn't need a confirmation box deleting some of theses from the code like the one for when you die and click restart level we don't need to confirm at that moment because of the only two options we have on that screen.
2. maybe get rid of the health bars over enemies, it can be process intensive on the computer having to check the enemies on screen and do the math in the split seconds while your firing down range
3. The bullet animations, I like the idea of them being tracer like rounds but i think this also maybe adding to the lag the game gives. again going back in line with twos point of lag to produce the visual feedback
Like i said before its a great game, I like the concept and the art style you went with going into the project but I think the stylization came before the games ability to run somewhere in production. It might be simply the stuff I listed above all the code for some of that extra stuff might be bogging down the computer.
Love to see how your work progresses from here mate