I love the composition, and the planet are really high quality! great stuff! One little crit, if you look closely at the near planet surface, the mountains are shaded in reverse (from the texture having shadows baked into it )
Oh and I would like to second that request for a sun tutorial - you're flares are looking so damn good lately, I gotta see how you do it
I absolutely love this - it has a nice old-school sci-fi vibe to it. That third moon/planet might be better placed behind the second's rings, but beyond that, this looks great. I also like how subtle the nebula is and how serene the colors are.