I thought Vau was merely average but I went for lunch. Food was good but not exceptional and the service was shoddy, with staff more keen on coming into the dining room (where only 2 other tables were occupied) only to bring food and remove plates and spend the rest of the time at the back of the restaurant talking to one another.
I have heard that the restaurant in the Schlosshotel in Grunewald is very nice as is the restaurant in the Regent (when it was a Four Seasons, Seasons restaurant was excellent).
I also liked Aigner, right across the street from the Regent. Great food and is a little more casual.