Gretchen,
I took the tour two winters ago, and I want to add this comment to the mix: our guide slightly altered the written itinerary by giving us our Seine boat tickets but by saying we would not do it as a group. Which was fine. A guy from the tour and I went one of the evenings after dinner. And maybe the itinerary has changed, but we did not have a quick overview of d'Orsay. We were on our own at that point, and it was New Year's Day, so maybe that had something to do with it (many of the other museums are closed that day, so the crowds are bigger). I could kick myself for not visiting d'Orsay a different time or adding a day on after the tour to visit it because I love Impressionism.
I really enjoyed the Marais district. Wow sights, no. Quiet and a walking tour focused on history, yes. Regarding the water lilies, I'd taken a number of art history electives in college, and I thought the explanation of Monet's work was overkill. So, be warned, it's a detailed explanation. I thought the Louvre tour was the right amount of information and the right length. We were on our own for Cluny.
My long-winded point is that you will see or have access to everything on the itinerary but know that your guide may mix it up. To me, the London and Rome tours are a little more history, and a little less art. All have a bit of art, but Paris seems to have the most.