When something happens disappointingly, it is not as good as you hoped. You had a picture in your head — bigger, better, kinder, more exciting — and the real thing falls short. People often put it after a verb: the team played disappointingly; sales grew disappointingly slowly. You can also open with it: Disappointingly, only three people came. Though actually, the word does not always mean the thing itself is terrible. A meal can be fine and still feel disappointingly small if you were hungry. A day can be all right and still end disappointingly if you wanted a surprise. It is a little more at home in writing and careful speech than a sigh and “what a shame,” but ordinary people use it too.