Location, location, location ... it is a very large apartment, by Paris standards, and is in an amazing location. A few blocks from Notre Dame ... a few blocks from Pompidou, on an amazing square with cafes galore. It is truly living the Paris city life staying there - which, if that's what you want, you will love it.
Marie is an amazing hostess - very communicative, responsive and accommodating. I can't say enough good things about her.
The only potentially negative thing I'd point out is that the cafes and bars, which are right below the living room and kitchen windows, are outdoor - and so the patrons are outside smoking and drinking until late at night. If you wish to have windows open - it's loud and the smoke will waft in. With the windows closed, it's almost eerily silent. The windows and outside shades are remarkably good. If you like to be out there eating, drinking and smoking - this is probably a positive for you ... if not, it's the only thing to think about. Everything else about the place is really amazing.