Perfect, perfect location in the historical part of Vienna. Close to all main attractions. Very quiet, clean and modern hotel. I also liked the style chosen, good looking and nicely renowated.
We requested three rooms near each other (three couples), because we had a celebration trip, but didn't succeed to get that. Hotel didn't pay any attention to my request even they answered to my mail saying they do their best (a small thing, but still matters - perhaps a wish for happy celebrations etc, but nothing). Front desk functioned, but staff was not specially friendly. Two young receptionist didn't even know, where the Hundertwasser House was - what!!! They googled it and gave us a map with a point marked after that. No information how to get there...
The hotel breakfast is very expensive. You'll find nearby good cafees with a wide range of breakfasts, so don't pay extra by staying at hotel restaurant. Also prices at the hotel bar were higher than elsewhere.
We had a very nice room, a quiet and very clean bathroom and a big window with large ledge. Wifi was quick and easy. Elevators worked perfectly. Front desk ordered us a taxi for six to the airport, comfortable and not expensive.
Would highly recommend the hotel, still a long way to five stars because of the small things. The small things are usually taken care of at five star hotels - because they know, those things make you something special. Good luck with upgrading!