I think this is a beautiful piece. Technically it's perfect. Nothing in it looks man-made or unfinished, at least not at this resolution.
I have three issues with it, and all are closely related, conjoined twins sort of issues. Basically, while it's beautiful and very well made, it is a little boring.
The composision is all diagonal lines. If you took a pinstriped fabric and held it against the image at an angle, it would line up with the way the eye sees this piece. It has a little bit of a flow, but not much. The planet's curve takes me from the left edge to the top edge. The nebula and asteroid belt take me from the bottom edge to the top edge. There's no one thing, or one chain of things, that leads me around the image.
There's no "heat". It's all cool tones, greens, blues, a couple of violets and dull yellows. There are no bright spots and nothing eye-catching. The strongest thing in the image is the planet. A dull pallate can be rather boring.
Last, the image doesn't tell a story. There's no action, no forming planets, no old planets. It's just...kinda there.
I said that all three issues were closely related. Composision and a couple bright colors would lend it more movement (more "story") and make it interesting. In my experiance, good composision (and sometimes color choice) come out of "story". That just means you take a few seconds out of someone's life (this would be a few millinia for a star system) and ask what happened just before, during and what will happen just after the image.
Try, say, giving the planet a moon (maybe even a half-destroyed moon) in the middle left ,between the planet and the asteroid belt, and then putting a comet in the upper right area. Something along those lines. Give the image more movement and "story" and a couple of bright spots.