I think the 500ml bottle must have sat on the shelf too long. I got little carbonation and virtually no head. The beer is a very nice color, clear dark brown with hints of red. Unfortunately it neither smelled nor tasted of anything much. It was drinkable but was less flavorful than I'd expect even from a lager.
My experience really didn't match those of other reviewers (http://beeradvocate.com/beer/profile/39/134); perhaps it should be served warm (and fresh.)
More reviews: http://www.ratebeer.com/beer/ayinger-altbairisch-dunkel/2019/