Can't have a better location, quiet street in the Marais, easy and central to most transportation. Boulangerie across the street was prefect for the morning pain au chocolat! Restaurant across the street was also delicious.
As others have stated, the upper loft ceiling height can be challenging for those over 6 feet (1.8m) high. You'll have to duck when transitioning into the shower/bathtub room.
Be a tad mindful if you are prone to tripping easily at night on your way to the toilet, or have some mobility issues. Getting up and down the inside loft stairs and some stone floor steps might be unexpected in low light. Plumbing fixtures are creative, and takes a bit to get used to, but we appreciated the fun design of the flat.
The neighbors above we think, have small children. Can be some clomping/stomping noises from the ceiling in the mornings. Not terrible, but just be mindful if you're sensitive to it.
Also, it's an inside, lower floor apartment that has a couple windows onto the entrance courtyard, but otherwise there isn't a whole lot of natural sun light if you're looking for that.