This apartment was exactly as described and met our needs perfectly. As others have mentioned the three flights of stairs could be a problem for some people (especially with your luggage) and the streets are quite noisy at night (particularly on the weekend); however we expected that and enjoyed the apartment. The location near the metro and steps away from the beautiful Montmartre area was perfect.
The big problem was a lack of coordination from the owners. We were given a code for the gate and told that someone would meet us upon our arrival and would then plan for our departure. Getting through the gate with the code worked fine; however after the gate there are two doors which lead to two different buildings and each with another code. We were never told which door to take and didn't have the second code? Luckily for us a man left the building about 5 minutes later and told us that the apartment for rent was through that door on the top floor.
Once on the top floor we were told that it was the apartment on the right. No answer, so we sit down and wait for someone to show up. After about 30 minutes three cleaning ladies emerge from the apartment on the left and see us, they then offer me a set of keys. I check inside the apartment and indeed it turns out to be the apartment on the left... not right. I'm trying to communicate with the cleaning ladies to get some info about our departure and the balance of Euros which we owed upon arrival but not one of the three speak French or English! They only spoke an Asian language which I do not! One of the ladies finally calls someone on her cell phone and hands it to me. This person turns out to be the woman who was supposed to meet us and tells me to leave the Euros with the cleaning ladies and that all instructions will be on the counter inside. When I go to give the cleaning lady the money she doesn't want to take it and still doesn't understand. She finally calls back the woman and is explained that she must take the money.
Basically one of the most complicated check-ins I've ever experienced... and all this after being awake for more than 24 hours with the flight and all. I contacted the same woman more than once during our stay to try and plan our check-out and only heard back on the last day telling us to leave the keys on the counter and close the door. So basically we never met or saw any one of the owners.
After all that, as I said, the apartment was nice.