The apartment is fantastic.
First, location. It's a couple minutes walk from St Michel/ Notre Dame RER and Metro stop. So super easy if you're coming in from Charles De Gaulle airport or the Gare Du Nord. No need for a taxi. It's also the same station for the train to Versailles. You can walk along the Seine to the Louver, Musee d'Orsay, Notre Dame, and you're minutes from the cafes and restaurants of the Left Bank. We really enjoyed morning coffee at close by Malongo Café (for a more American sized latte) and Carton Bakery a little further along Rue St Andre des Arts with the best pain au chocolate ever. Also dinners at local restaurants Le Bistro des Augustins and La Table des Arts (superb bistro, so much better than the tourist traps a few blocks away).
Secondly, the apartment itself. In a 19c (I'm guessing) building with a court-yard, classic Paris. Off a quiet street, yet just a few meters from the river. Apartment is on the top floor (no escalator so you need to like stairs, but again very atmospheric and I liked the old prints on the walls) and was very quiet - despite being a 5 minute walk from the tourist madness of Place St Michel (my wife stayed at a hotel in that area which had music blasting until 2am - here there was the only the sound of seagulls and pigeons). Apartment is quiet, light (east facing windows) with a view (at an angle) of the gothic spire of St Chapelle - what more could you want? Inside is comfortable, good kitchen and laundry machine, strong WiFi, clean bathroom, plenty of shelving, beds comfortable - and very quirky antique paintings/sculpture. It got cold one night and we turned on the heat in one bedroom, worked perfectly. A joy to stay in with plenty of room for dinner and relaxing for 4 people. I really appreciated the guide books. The roses in the kitchen were a nice touch. The place was spotlessly clean.
Check in was super easy (a person was waiting for us outside the gate to let us in and show us around) and communications with Camille were very easy (she checked up on us during the visit and quickly answered all messages). I would definitely stay again when I'm next in Paris.