Perfect location for visiting Paris! You're within very quick walking distance of the Sorbonne, Cluny Museum and Saint Chappel. Notre Dame and the Louvre are not much further. Beyond that, there are so many amazing restaurants (particularly oyster-based!) and bars nearby--we felt like we barely had to get on the the metro! You're also super close to the RER station where you get the train to Versailles, which was handy.
The apartment itself has a great layout and enough space for two couples comfortably. The shower was great, and it was nice to have the terrace to sit on (though as it's overlooked by several other apartments, we didn't want to be out there too long/late talking, as it felt disruptive). The apartment also stayed nicely cool during very warm summer days.
The only downside is that the bedrooms face onto the smaller back street, which has a surprising amount of loud traffic on it. Every morning around 6am (inc Saturday), the trash truck would rumble down the road waking up my husband. It might be better when the windows don't have to be open, but as it was a series of warm summers nights, we had to keep them open.
Otherwise, terrific location and nice space! Definitely recommended!