We were there this past January as well. We hit a beautiful weather streak. It had been cold before we got there, then the whole time we were there it was sunny and 80's every day. On our last day, it rained, then after we left I guess it got pretty nasty and cold.
The weather is kind of hit and miss, but most likely you will encounter some refurbs and shorter park hours. If you go in early January you'll have the marathon to contend with. We just steered clear of the parks on that day and we were fine.
Park hours a shorter, but shorter lines evens it out a bit. IMO January is a great time to go.