Our very first trip to WDW was the very end of January/early February a few years back. It was amazing! Like a dream. The parks were very calm and not busy at all. We were able to walk right onto rides/attractions at MK even at 11:00 in the morning (ok, not headliners, but it was still thrilling to meet Ariel without a wait). The weather was quite warm that year. We had a few days of near-90 temperatures (although evening were cooler probably because the sun sets earlier in January). So clearly the weather can vary a lot! If you can avoid the busy times (New Years/very beginning of January and the marathon...maybe busy for MLK weekend? We've never been that weekend), it's a great month to go. Nice weather and lower crowd levels!