I'm local-ish and went with my partner between Christmas and new year 
It was beautifully sunny but bitterly cold (as others have mentioned).
We went on the spur of the moment but if you have time to plan definitely do it with Tesco Clubcard vouchers if you are able, otherwise it's c.£20 for an adult ticket.
Last time we went (winter 2012) there were lots of talks and feedings where you could experience the animals close up. On that occasion we saw the elephants being taken for a walk on the perimeter road, the elephant talk and feeding, interactive lemur walk, sealion show etc.
This time there were no feedings listed in the leaflet and map at all - just talks outside the enclosures. By arriving at 11.15am (got tickets and entry by 11.30am) we seemed to have missed about half of the day's (limited) talks 
The walkthrough lemur experience was closed and the elephants remained in their enclosure. The sea lion arena was empty 
I expected a reduced winter schedule but I would say it was very reduced. Surely some animals still needed feeding?
selfish
On reflection it should have occurred to me that the lemur walk (my favourite) would be closed but I would've appreciated clearer info on the website or the ticket queue.
One of my highlights is seeing the keepers interact with the animals they care for.
We had a nice time and got to see a good variety of animals however our visit ended sooner than anticipated 