Played it and it was great and I have some ideas for the music since more and more enemies spawn as you play and you really have to try your best to run away and not let them kill you. maybe some fast paced music would get the player's heart beating and because of the style i'd also think an 8 - Bit song would work, another thing is the lighting, it gives of a very serious vibe which is really good btw so a more serious (not upbeat or happy) song would fit.
I recommend using this for the levels (and trailer) but don't play it too often as it might get annoying for the player (It's also a perfect loop but again it might get annoying to the player or not your choice)
And this could be for the Menu Good Luck!
These are just recommendations you don't have to actually choose them I'll be fine with it if you don't as it is your game