The space: the bed was very comfortable, the wifi was fast and there seemed to be everything you would need to make meals in the kitchen (we mainly ate out but certainly used the cheese and bread knives and wine glasses!) The bathroom has a typical European shower. The stairs were no problem for us, good to work off all the pastries! Lovely view from the windows too, we saw the Bastille Day plane fly overs. There was a fan and at about 25 degrees we weren't too hot with the windows shut.
Nadia and Olivier: Nadia mapped out two long walking routes to see the sights from the apartment and she very helpfully pointed out restaurants and patisseries. They were very helpful with bags and washing and were lovely people. I would say the idea of AirBnB is based on these too, the absolute love of showing people around your home city!! We can't thank you enough for the excellent experience you gave us.
The location: perfect! So close to the Louvre and as above, Nadia helped us with a route to walk through all the major gardens, past the major sights. It is a great location to be close to touristy things but it also felt like you were living where the Parisians lived. It's also close to Montmarte to walk up to Sacre Coeur with plenty of delicious dinner places in the way back down the hill.
Overall: great apartment! Definitely recommend!