Tell ya what Simon, the overall look of this image at modest viewing size is really impressive, I really like the composition and the whole nebula has rarely looked so dramatic, so well done on this.
I think the only thing stopping this from being a real corker is that you have flattened the highlights a bit and over dimmed the Keyhole area and maybe skewed the curves a bit too..?
But don't get me wrong, it looks bloody good regardless
Mike