We had a wonderful stay at Alex & Ece's beautiful apartment. The location is superb - right next to a metro station and very easy to reach from the Gare du Nord - and there's lots to see and do within walking distance (including a very handy supermarket and some excellent restaurants).
There was a certain degree of noise at night (sirens, rubbish trucks etc), but no more than you would expect from such a central location.
The apartment itself is lovely and light filled, and felt a perfect size for me, my husband and our two children. Decent kitchen, two very nice bathrooms - and an absolutely tiny toilet!
We felt very fortunate to have stayed here, and would recommend it wholeheartedly.