I like the shot also. I think it's very close to where it needs to be. The one area the confuses my eyes is around Shadow's mouth and collar. It's so hard to discern what is what, that it's distracting to me. My eyes spend more time there, than on the subjects.
So, if there were a way to differentiate that area... maybe lightening the muzzle a bit and hiding the collar or tag.... maybe just the tag.
I'm sure you could play with the background also. But, since it's already a bit blurred, it really isn't necessary. You could try to reproduce the natural shadow/vignette from the left over to the right. That may bring some balance as well.