really good use of those brushes there, the sky looks really cool, only problem i got with the piece is once you detail it too much, like before you click to look at it full res it looks fucking amazing, once you look at it closely alot of details from the background look weirdly textured.
i would probably recommend experimenting and trying ways to make the background some blur to not draw too much attention without losing the texture.
anyway idk i'm fucking awful at giving critic but hope it helped.