A totally charming apartment in the best location, which is very well equipped. Right on the river, it is wonderfully placed for exploring central Paris. You are literally five minutes from Notre Dame or the Place Saint Michel to pick up the metro, but we walked nearly everywhere.
Like most Paris apartments it is on the compact side but more than big enough to be completely comfortable for our family of four, and the little kitchen has everything you need if you want to stay in and cook.
Because of the stairs I couldn't recommend for anyone with restricted mobility (sorry) but for everyone else I can't think of a better base for visiting Paris.