We really enjoyed our stay in Isabelle's apartment. The location was perfect! It was very close to cafes, boulangeries, the markets, the metro, the Picasso Museum, and everything that is great about the Le Marais area of Paris.
The weather was very hot during our stay in early August--above 30C/86F several days, and as high as 36C/96F one day. Thankfully, Isabelle left us two very good portable AC units, to keep the main bedrooms cool.
Since the apartment is on the top floor, it does generally get good air flow. The windows are huge and can be fully opened. We kept them wide open during our entire stay and it helped make the apartment pleasant from morning until mid-afternoon even on hot days.
The kitchen has been remodeled more recently, with nice appliances and layout.
The building does have an elevator/lift that takes you to one floor below Isabelle's apartment, so you will need to climb one flight of stairs.
The terrace is a nice place to enjoy a drink or coffee.
While there are two bathrooms, there is just one toilet.
Two nice boulangeries, La Petite Ile and DuPain, are just a short walk. We particularly enjoyed meals at Le Progres, but all of the cafes are good. Two supermarkets, FranPrix and Carrefour, are within two blocks.
Overall, this apartment was a great experience for our family, and a very good value.