Check the crowd calendars and you'll that it gets crowded around a holiday. Otherwise, Jan-Feb is a great time to go to WDW. We've gone many times during the winter and enjoyed less crowds and cooler weather. While usually nice during the day, it could be cold at night (we live in Hawaii so anything below 70* is chilly, and below 60* is cold! but you might find it pleasant) so be sure to bring clothes for cooler weather. It's been more crowded in recent years due to the S American tour groups, but that's mostly noticeable at the MK.
You'll have a great time, I know!