Simple, but effective. I think this is a great example of coming up with something accomplishable and just making it well. (Instead of, you know, making a bloated, buggy, over-scoped mess that no one would bother to play all the way through anyway. But none of us ever do that, right?)
Don't know that I totally get how the theme comes through, besides maybe just the game itself being 2D. But honestly, I couldn't care less. This was just good fun!