We went the middle of January this year. Some of the days we were happy walking around in a fleece but a couple of the days were VERY cold and you needed fleece, coat, hat, scarves and gloves!! As it was Magic Unlimited there were a lot of English families there. You certainly don't get the queues you see in the summer (although we went Monday - Friday and the Friday there were a lot of people checking in so I would imagine the weekends were much busier) but it is nice to be able to stay on some of the rides for as long as you like, especially if you're feet are tired and want a rest or you are cold and want a warm up! If you pack a mixture of clothes or wear layers it is better as you can add/take away a layer or two. I think the longest queue time we saw while we were there was 20 minutes but many were like 5 minutes or however long it takes you to walk to the ride entrance.