i have been to paris, and to france a number of times, always in winter. winter is game season. we have gone specifically for game season a couple of times.
paris is 10-20degrees warmer than NYC in winter. almost never goes below 32F in paris. most of the touristy riff raff is home. tourists do appear around christmas, as do a huge number of students. day and light is very short. restaurant reservations are much more available. in nyc, i recall some big trade shows in javits in dec. the place is still packed, and cabs can be impossible. get a bus map.
the tops of the double decker busses are empty.