Feedback on a very much WIP picture for concept art

I've been working on this picture for the past few weeks, slowly trying to complete it as cleanly as possible. I've not really had any criticism on it, but I know there's a lot more I can improve on, specifically in capturing the female form. Any criticism (harsh or otherwise) would be greatly appreciated.

Featured in the picture are the characters Belthra and Gyrheim along with their cathedral

This is a concept image for a faction called the Order of Lies in manga I'd like to complete some day.