Hello Julie and Sue,
I went on this trip in July and had a wonderful time, although very hot! The concert was so good that 5 of us booked for another the following night. The hotel recommended a very good one, made the reservations and even booked a taxi for us. The other highlight was the Schonbruun Palace and in particular the Strudel Factor not to be missed!
Two tips; virtually everywhere took Euros and secondly, if going on the optional evening cruise, use midge repellant!!!
Have a great time.
David.