The good: The location is excellent--Seven Dials has many independent shops and restaurants, and has both a quaint and hip village feel to it, even though you're smack in the middle of London, and easy walking distance to Soho, Covent Garden, Bloomsbury, and other great neighborhoods. Multiple tube stops are also very close. The apartment is exactly as it's represented in the pictures: modern, clean, a little spare with no frills.
The bad: As others have noted, the noise in the neighborhood can be a problem. As I was there in the summer, and it was fairly hot during my stay, I needed to sleep with the windows open. Nights were not a problem, but early mornings were. Each morning I was awakened between 5 & 6 because of the noise of deliveries, trash pick-up, or early morning work happening on the street. And the bed is just a few inches away from the windows on the street.
There were a few other minor issues during my stay (broken window shade, loose toilet seat, slow drain in the shower) that Sergio was quick to respond to. Communication with him was very good.
Bottom line: the flat is very nice and in a great neighborhood, but the early morning noise in the neighborhood could be a problem, especially in the summer.