See, now when you ask for C&C, you really need to accept it. And I think the top is way to saturated, but seeing your other stuffthat seems to be your style (Or maybe that is MinorThreat with the saturated orange/red grunge?).

The mountains don't exactly look so great. They just seem to stop. I understand that mountains do just stop in real life, but I just can't put my finger on what doesn't look so great.

But definately change the border, it lookd spretty bad. Just take out the white lines, that would look better.

And the Planet does looks pretty flat, did you only spherize it 50%? Do it again.

And the absolute last, and probobly the most important - did you make the nebulas? Or did you just use a premade brush? It looks like a brush, and using premade brushes for stuff like this is worse than filter-whoring in my oppinion.

But other than those little things, it does look good. Its just a bunch of little things that bother me, no really big things other than the planets looking sort of flat.