This review is short because I really have no complaints. Rooms are very spacious, comfortable and in the typical Renaissance decor. The staff could not have been more helpful in helping us get to the airport and make dinner reservations for us. The location is great and very close to Termini is you are travelling outside of Rome by train.
I would go back in a heartbeat, not because I loved the decor (a bit old fashioned for me) but because of the unparalleled service the St. Regis provides.