Giverny or not?
 

We went to Giverny in September 1992 and, although it
was interesting because of its associations with
Monet, it certainly doesn't stand on its own as a
garden. Quite a tourbus crowd the day we were there.
Also it is quite close to a noisy highway. So in the
end I suppose it comes down to how much the
association with Monet matters to you.

There is a museum right in Paris, called I believe,
Marmotten, full of Monet, which makes the trip to
Giverny unecessary. We spent several hours there and
then stopped at a Salon de Tee near the Metro stop on
our way back to the downtown area.

Well, I'd like to differ with the other contestants here---Giverny isn't at it's absolute best in the fall, but the gardens are very beautiful---and don't forget the house itself, which is crammed with Japanese prints (Monet was evidently fascinated), and has an incredible kitchen and dining room. I don't know if you've studied Monet's work or not, but being in the garden he so scrupulously designed can really hit home if you're at all familiar with his paintings. Color, texture, light, patterns---that garden is no accident. But if this is your first trip to Paris, and Monet isn't a passion, I'd vote for the Musee d'Orsay or the Orangerie's oval room filled with a series of "Water Lilies."
If you'd like to take a short trip outside the city (besides the gilded glut of Versailles), Chartres (amazing cathedral, and you can arrange a whip-smart tour with an expat Brit) is a good bet. Have a great trip.

I'm going to say not for these people. They are definately not the kind of people who obey men with hailers.

To me the most amazing part of Giverny is the lower garden and lily pond. How can anyone stand there and look across that pond at the Japanese bridge and the water lilies and not get chills having seen so many wonderful Monet paintings depicting those very real scenes. It is also fascinating because of the incredible amount of Japanese art all over the house which really explains so much about Monet's style. I've been twice and will probably return again to marvel at it all.