Thomas' apartment was nice and the location was great (very near the Montmartre-neighbourhood, and with good connections to the metro).
Everything was clean and cosy in the apartment, the only minus was that the apartment was a bit cold (we were there in the beginning of May. But I think that must be quite common in all apartments of Paris ;) The apartment was comfortable and spacious.
There was no major issues with the cleanliness; it was not tip-top-shiny, but neat and clean (and we were travelling with a two-year-old, so our standards may be a little bit higher than the usual).
The location was very convenient (especially if you want to spend time in the Montmartre-area) which is located very near. The closest metro-station is very near (with two metro-lines, 2 and 4) and the Gare du Nord -station is also not very far. The street on which the apartment is located was a little bit noisy, but the apartment faces the inner court of the building, which was very calm. The neighbourhood is not the calmest one, but we did feel it was quite safe.