Excellent apartment centrally located in Trastevere and an easy walk to the historic center of Rome. For two people it was spacious and the kitchen, while compact, had everything we needed. Giulio met us and made sure we had everything, gave us some excellent restaurant recommendations (Impiccetta), and walked us to the supermarket so we could buy some basic groceries. All told, a very good choice for anybody wanting to explore this part of Rome (and you definitely should).
As others have pointed out, it's up two flights of stairs with no elevator so if mobility is an issue, you may want to look somewhere else. Also, there's no washing machine so you'll have to use one of the various laundromats in the area if you need to do laundry.
I do recommend the car from the airport that Giulio set up for us (there and back in fact). It's only slightly more expensive than public transport and a heck of a lot nicer, especially after a long flight.