If you want an authentic experience of what it is like to live in Paris in true style, this is your place.
I'll St Louis is the perfect place to stay if you want to be in the center of things, but not have all the crowds outside your door all of the time (you can walk to them in 5-10 minutes).
The walk up to the top is worth it every time you look out the window at the Seine, Notre D, and Eiffel tower.