Some people made a couple of suggestions. The two most important ones being the reflection of the planets in the river, and the detailing of the surface and the clouds on the biggest planet.
(If you're not interested in detailed explanations you should skip ahead to the image)
About the detailing, it was suggested that the clouds (the ones on the big green planet in the background) should have more detail than they have now, since they are above the surface of the planet and therefor closer to the viewer's eye than the surface. On this I had to disagree.
If you look at photo's from Earth taken from space, one will notice that clouds are more blurry than the surface. This has a couple of reasons.
First of all the issue of the clouds being closer to the viewer's eye than the surface.
This is true. However, clouds are only between a couple of hundred of meters and a couple of kilometers from the surface. The planet itself would be several thousands or even millions of kilometers from the viewer's eye. Over such huge distances, the relative small difference in distance between the planet surface and the clouds would be negligible and hardly noticeable.
Secondly, clouds are fuzzy by nature, seeing they exist of water vapor. Some clouds are sharper than others and may have more detail in them, but due to the fact that they are mostly made up of only white and gray shades that flow into each other, the detailing is far from what you would find on a planet surface. A planet surface however, has numerous sharp details. Roads, mountain ridges and the shadows created by them, rivers, sharp contrast in colors in general, cities, etc. etc. And even from quite some distance like in space, you would be able to see this detail. Like you see it on those pictures of our own planet Earth.
This makes that a planet surface would be more detailed than cloud layers, seen from space.
Now, the reflection of the planets in the river.
This was spot on. After having a closer look, the reflection was way off. The part of the reflection you could actually see did not make any sense.
So I have redone the reflection altogether. I hope it looks better this way. Let me know what you think once again.
P.S.:
I just wanted to let you know that I really appreciate each and every comment made. The critical ones even more than the nice ones. Because this is how I second guess my own work and find things to improve. When working on images for hours at a time, you tend to not see certain things anymore. Then when you publish it, people will suddenly notice those things I myself had lost sight of in the process. That is why I think other people their first impressions are very helpful in improving my work. So please keep those comments coming! And don't be afraid to be critical, I can take it. If you think it sucks, just go ahead and say it.

Ok so here's the edited version:
Retired.
"Never argue with an idiot, you will have to lower yourself to their standard and they will beat you with experience"