A great deal of attention to detail, and it tells it's own story, truly excellent work.
If I were to write a book, this illustration would be the quality I would be looking for, and I am sure that with all the details you have included, you are or should be an excellent writer. Very professional work. If you could make a portfolio in the same style, it WOULD BE, if it not already has, be accepted on a high quality publishing level. Please let me know if you have any similar themes of paintings please - if you want to. Superb.