I managed to get down to Winter Wonderland yesterday and despite the rain managed to get on a fair few things.
Olympia Looping was amazing. It was far smoother than I was expecting (smoother than some of Merlin's coasters!) and was a good overall ride. I did notice what others have mentioned with the restraints, on my ride I felt them push down as I went through the first inversion. It's certainly a ride I'd like to do again and I hope it returns next year.
There did seem to be a decent range of rides, although it was a shame Break Dance and Airwolf didn't make a return this year. XXL and Wilde Maus were as good as ever.
One thing to be aware of if you are planning a visit us just how busy it gets. Even in heavy rain the event was still extremely busy with all the ticketed attractions such as the Ice Kingdom and Ice Skating sold out. There were also issues in the tube with the Piccadilly Line experiencing long delays and several stations closed due to the volume of people on the line so it's definitely worth checking before you go.