This is an interesting one. My very first impression of it was that something was lacklustre about it, as if it were a little flat. But then I gazed at a bit longer and, as if coming to the right exposure, a much greater depth showed itself and made the piece a lot more enjoyable. This is somewhat double-sided - on the one hand, it develops a great sense of depth with contemplation, and on the other hand, there is a lack of highlights in the darkness which eludes one's immediate grasping of depth. Still, it is this very ambivalence which makes it so interesting, a great intention there, since it does make it a piece which makes a more lasting impression than many others, albeit not straight away.
Concerning immediate impression, the lack of light interaction with the edges of the nebulous haze to show reflectivity, and the sense of clone-brushing here and there (i.e. left of the stellar nursery) does bring it down. It may understandably be difficult to add such alterations to depth without taking away the contemplative sense of the piece, but the cloud repetition could at least be modified. But even though there is critique concerning that, there is still much else which is quite nice about this piece.
The starfield, for one, and the subtle gradients of light and hue about the piece all add to the overall splendour of this piece, especially in its contemplation. The planets, although they seem to be setup very simplistically, do have an enjoyable sense of counterbalance between each other in the composition. In this way, the minimalism of the piece is essential the aforementioned contemplative quality of it. Such a quality is what one could worry about losing with further alterations, due to the fragile nature of minimalism when adding and changing things. Still, it could be possible to add just here and there a few well-placed streams of light reflecting off the nebulae, and conjunction with the slight variation of texture in parts.
Although there are minor details which could be improved, not to change the piece so much as to draw more people into the actual contemplation of it, the piece is as it stands another good piece of artwork from you. It is this difficult balance of a flat initial impression with a thoroughly contemplative impression of depth which makes this particularly difficult to rate, and yet which makes it work. Thus my suggestions that, if it were to be modified, to do so only to compliment the furtherance of others contemplating it - thus, minimal changes for a minimal piece. With this in mind, excellent work, and it would be a pleasure to see some more works with such a contemplative aesthetic - so, I say well done!