She is the Queen of England. Just how much input do you think the photographer had? Do you think he said "Smile" and refused to take the shot until Elizabeth sported a toothy grin? I don't think so. I'm sure he made decisions as to the lighting and positioning in the frame, and maybe, just maybe, if they were sitting or standing. Otherwise, he was just the guy pressing the shutter.
Well, I like the shot. I think the lighting is quite effective - it appears to be natural. I also like the way the photographer handled the lighting on the background; just enough falls back there for us to make out the decor. As for the subjects being off center, to me, it makes the shot more interesting. Granted, their expressions are rather wooden, but it bespeaks the dignity of their positions. On the whole, I find the photo quite effective; but, hey, that's just me.