He's gorgeous and really looks like he's smiling! You can really see their power in this shot, with those huge antlers and the bulk around his neck but there's also the nice juxtaposition happening with his friendly face.
Certainly a magnificent animal, and you have clearly managed to get very close. The woodland in the background provides good context, but I do find the composition slightly awkward - its all subjective, but I would probably have pulled back somewhat to get more of the stag into the frame.