The location is great, across from an amazing chocolate shop and next to the Picasso Museum!
But at $636 per night (when we booked), this was one of the most expensive apartments in the Marais, and we expected a lot more value for money: even though the apartment sleeps 6, there are _exactly_ 6 glasses, 6 mugs, 6 towels, etc. so you constantly have to wash in order to reuse. In the same vein, the WiFi is slow, and only works on the main floor; and the TVs in the apartment only play French cable stations...
The listing is not very accurate: the apartment only has two toilets, one of which is accessible through the living room (hence not private at all), and the other is in the basement and relies on a noisy pump to work. Also, the bedrooms are not "real" bedrooms, as only one of the three has windows. The other two are really just enclosed sealed spaced with beds, one of which doesn't even have a closet. The nice outside area you see in the pictures is indeed very pretty, but off limits. The apartment only has access to a narrow ground-floor balcony which we didn't as it only fits one or two people.
In summary, we would stay here again if we had to, but would look for other options first.