Arnaud and Gary's place is stylish, comfortable, and wonderfully located. The neighborhood is hip and filled with great restaurants and shops. Much of Paris is easy walking distance, and of course there's the Metro. Across the street is a supermarket, but also a nice shared market with greengrocers and specialty shops.
As others have mentioned, the two drawbacks are (1) the considerable noise from the bar across the street (it closes down at 11 on weeknights, but stays open until one on weekends); and (2) the very narrow winding staircase. If you're not fairly agile, the latter could be dangerous. Also, the bathroom is divided, with the toilet on the main floor, but the shower and sink in the basement with the bedroom.
For me, the apartment was great, and these were all minor inconveniences. It's charming and bright, and is well-priced, especially considering that it has modern AC and heat.