To quote Audrey Hepburn, Paris is ALWAYS a good idea. I love the Bird Market, the sidewalk cafes, and people watching at the fountains across from the Eiffel Tower. That said, the parks are amazing - Europe really knows how to make parks - and the museums are to die for. You could spend a month at the Louvre and not see it all.
I could go on and on, but the fact remains that Paris is one of the world's greatest cities.