Most of the other reviews get this right.
A very authentic, atmospheric little place place right in the heart of Rome.
If you prefer sparkling white characterless hotel rooms, this will not be for you, and the furnishings may seem rather tired. But that's the point, it's somewhere that has been genuinely lived in and that's why I loved it!
For central Rome it's remarkably quiet. In the late evening, there's the inevitable chat in the small street outside from people coming back from restaurants, etc, but by the small hours of the night it's very peaceful. And you could spend weeks exploring interesting parts of Rome without needing to take public transport (though there's a useful bus stop less than five minutes away). An excellent small place for coffee is almost on the doorstep and there are some decent restaurants nearby (I recommend Ristochicco, very close).
Finally, you'll find Marco to be molto simpatico.