My experience in apartment may be different from others as I was not there as a tourist, I live full time in Paris. I was actually working each day from the apartment and not touring the city like a visitor so I spent much more time in the apartment.
The good things: Lucas is a very nice man and his command of English is excellent, which makes communicating with him about the apartment very easy. The apartment is well located in Paris and has good access to subways nearby that allow you to get anywhere in the city. Finally the apartment is quite large, by Paris standards, and can fit multiple people.
The challenges: The apartment seems to be taken for granted and as a result seems rundown. There are many things that need to be updated for the apartment to be fully enjoyable. These things could be easily fixed but one has the sense that there is no desire to fix them.
The shower door doesn't close. The door to the Shower room doesn't stay closed. As mentioned by others, the couches need to be cleaned. The TV currently faces a wall and can't be turned so it's really not useful anywhere in the apartment.
The biggest issue for me was the heat as I was there mid-winter in January. There is just one small radiator in the entire apartment and as the apartment is below ground, it was quite cold down there. The temperature was below freezing most nights. Lucas very kindly brought me a space heater. Without the space heater, the apartment is a real challenge in January. Finally the plumbing seems to has problems as several signs in the bathroom threaten with warnings about disposal.
I think this apartment could be apartment, but with an update and someone taking the time to make it happen.