Benjamin's apartment is great. It's quite a bit bigger than we expected and has plenty of space for two people. The bathroom amenities are, in particular, very nice, with lots of hot water and a toilet that's effective and efficient, if you get my drift.
The view is as spectacular as other reviewers have said. You can easily see the Eiffel Tower, especially at night.
The internet connection in the apartment deserves special attention, since it's much faster than an average American connection. You won't have any problems emailing photos home to your friends.
The location in the Marais is good. The apartment is surrounded by plenty of restaurants and small shops, and the galleries of the Place des Vosges are basically across the street. There's a boulangerie downstairs and across the street, too. Although there are a lot of tourists in the area, it seems to be mostly Parisians who live there.
The building's concierge, Madame André, is very helpful and was essential throughout our stay. Note that she speaks only French, which may be problematic if you don't speak any.
In general, Benjamin's apartment is a nice place to stay, and I'd recommend it to anyone.