Lovely story! I have always been curious about ancient Egypt (had a slight obsession with it and its mythology as a child), so I was excited to see this story. I think you did a magnificent job of telling the story in a different setting but leaving Harry and Severus as themselves.
You also did a great job with giving the story life. When Severus told Harry about how he lost his power, I could imagine it really happening and fitting into canon. An enjoyable read from beginning to end.