The name is no more a mouthful than Leonardo da Vinci Rome Fuimincino Airport or Konrad Adenheur Cologne Bonn Airport, and with 27 destinations already announced in its first summer, it seems to be only helping raise the profile of the Doncaster Sheffield area by including the Robin Hood branding.
People will use probably use the location name (Doncaster Sheffield) as they do with Rome Fuimincino and Cologne Bonn, but the brand name (Robin Hood) adds value to the overseas market none the less.
In Cologne Bonn though, the name Bonn seems to be less used over time, e.g. easyjet rarely use it now. So over here it will be interesting to see which of Doncaster or Sheffield is more used by overseas travellers. Alternatively they could both be used as in Leeds Bradford, we'll have to wait and see.
I guess it might be fun to handle the first flight from Robin Hood Doncaster Sheffield Airport to Don Quixote Madrid Ciudad Real Airport, also due to be opening soon!