Love the art! And music is also really enjoyable and fit the game..
One bug that I noticed was that music in some parts is overlaping with other music. I think it happened after ending level. The music from level continues to play while the menu music starts playing..
And maybe the sound effects are a little to loud, eg. the machine gun in the 2nd level. The music is not clear then. But it can be subjective.
Overall nice idea, I would love to see the game polished and added more content , good job guys :)