Well first, your spoilers are just to links rather than images so I don't think you need the spoilers
In the first one I like how you've got the star flares all going the same direction, this is good many artists msss that up. Flares like that are caused by the aperture blades in a lens so will always line up. What method did you use to make them?
The second one looks like a fairly typical shooping, but well done, no seems or anything like that.
The third you did an excellent job on that planet. Very well done *applauds*
Something you might like to try: your stars are of pretty even density, try getting that to vary a bit. I would take your inspiration from shots of the milky way like this:
http://www.flickr.com/photos/ngc3372/1667753442/#