The pose is very cool, sharpness looks good, too. I would try to get more details in the underwings and chest using curves or Viveza if you use this plugin.
Did you already try to recover some details under the wings? There looks to be some colour noise, which is often the result of this when very underexposed. Too bad the light wasn't better, or at a better angle...it would have been nice to have those underwings, belly, and feet well lit. Good incoming pose though, you did well to freeze the action.
I like this shot very much. My only issue is the puffin's head is in the centre of the image. If is was composed with the head closer to the upper the right thirds intersection is maybe be even better.