The tone, rhythm, melodies, and mix are spot-on. I think you got a good sense of writing in these categories. However, as a stand alone piece (if not meant to be for a background piece in a game) it lacks in structure. As of now, this works great for a song if it had lyrics, but I expect a more interesting harmonic change/chord progression without it. By the end of any piece, a listener would need to get a sense of some kind of message that you're wishing to project in your music. Without lyrics, it makes it a bit more challenging to communicate what it is that you want to convey as this requires a bit more variety in "color," tone, tension/resolve, and interplay between melody and harmony. Sure, it's meant to go with the art piece that you have selected, but one still needs to hear the story you have in mind when you see this piece of art. Because after all, if we had ten people writing a piece of music for this artwork, it would all sound different. We need to know what you feel and what you want us to feel or think by hearing what you perceive this artwork to be. Otherwise, it becomes merely an exercise which will be less impactful/memorable for a listener. Unless a mindless, dance piece is the goal, which also isn't a bad thing as it certainly inspires in me to move along to it.
All that being said, it is a good piece. I'm merely offering certain advice in what I think would improve, not only the piece, but what would make this more impactful and an interesting experience for the listener. You could also simply throw my words away too--I'd respect that.