Although it is a bit too distracting to play with on full screen the idea for your background works pretty well. I like the combination system with weapons but I think you miss something. What I mean is, you should add something like a dropping chance on each enemy. You get random weapons, you try to combine them and you came up with a better (or worse) one than before.
There is potential in your weapon combination system, just be sure to expand it for further features.
PS: A restart option without the music cut would be loved.