This has got to be one of the most detailed and brilliant close ups of a galaxy I've ever seen. Perspective, texture, lighting, even down to the colors are unique, realistic, and spot on. Seriously, impressive job!
I looked through your gallery and to be honest, I don't have any specific crits. Just keep working at it, adding in details and refining your techniques. Don't be afraid to put any amount of time into a piece, the longer it takes the better it will be!