An excellent base for exploring Rome. Central, spacious, well equipped and comfortable (especially the bed!). It was also one of the cleanest places I have stayed.
Marcella arranged for us to be met at the airport and chauffeur driven in a plush car to the front door (it was Eur45 compared to a taxi at Eur30) but worth every penny. She met us on arrival, explained everything and then left us to ourselves with the assurance that she was only a call away if we needed any further help (we didn't as it was all so well prepared).
There is an excellent deli around the corner should you wish to self cater (highly recommended as the meat and cheese was bellissimo). Plenty of restaurants and bars nearby (avoid any within two streets of the tourist traps and book to make sure you get in) Piazza Navona is 3 streets away, the Pantheon a 5-10min walk. The Tiber is 10 mins walk, as is Campo di Fiori, and most of the old city. You can get buses/taxis from near Piazza Navona and there is bike hire around the corner (great for getting up to Villa Borghese or to the catacombs).
The only thing that may detract is the apartment is right above Bar del Fico which is open and popular to the early hour. This means there is quite a bit of street noise. The double glazing is good and it was absolutely no problem for us as we were tired enough after walking round Rome each day to drop off as soon as we hit the bed. For light sleepers, you may want to stay up late or bring ear plugs, but it really wasn't a problem for us.
Would I rent Casa del Fico again ? Absolutely! 5 out of 5 for me ;)