We had a wonderful stay at the Principessa Isabella. The location was about a mile from the "downtown" Rome attractions which was just enough to feel like we weren't in the center of the madness but not so far away as to be prohibitive. There's a couple cute restaurants in the area and a beautiful park nearby, so it is a good location. The hotel was very clean.
The rooms were refreshed daily. The staff was wonderful. They spoke perfect English and were very warm to us every time they saw us. Breakfast is complimentary and served daily, and they had a nice spread of croissants, meats, eggs, yogurt, cereal and coffee and tea.
Our bed was huge, and the room was a nice size too. There was a giant soaking tub and a great shower. The only downside is that the walls and floors are rather thin (tiled, not carpeted), and we could hear our very loud neighbors morning and night. Mostly, this was not a problem, but there were two sleepless nights. We never approached the hotel about this because it wasn't a huge deal to us, but if you're a light sleeper or traveling with kids, this might be an issue. Otherwise, I have no complaints and would gladly recommend this hotel to anyone looking to visit Rome but not eager to stay right in the heart of the city.