First, the good stuff: the location is genuinely ideal, on a quai on Isle St-Louis which is close to everything. The person who helped us into the flat (Ken) was delightful and even without complaint made an extra trip to the flat to help us get the heat on.
Then, the maybe-you-will-like-maybe-you wont: the flat is eccentric in a mostly-charming way, parts of this may not suit you - the sections of the flat (the bathroom, etc) are separated only by muslin curtains; the plumbing is workable and clean but may frustrate Americans (the shower is only hand-held). Much of the mechanisms of the place (the heating) are weird to Americans - the things that look like radiators don't work in shoulder seasons (eg October), the things that look like TV's are in fact a second heating system, and some of them are hard to find (a second one behind a desk in the bedroom).
Finally, the stuff that is harder to accept - 1) the stove was not working at ALL, since the gas had been worked on but the inspector had not arrived to approve its restart; 2) the lighting was eccentric (the light next to the bed on the left sometimes worked and sometimes didn't, come to find out that if the master switch by the door was turned off, the light didn't work, although the one on the right did!) 3) the communication with the owner was poor - we sent a note on 9/17 asking about staying an extra night but NEVER heard back either way, and we were not warned about the stove being unavailable. Ken said he didn't know, thought she might be still on August holiday (this was on the last day of September!).