It is great. There are some masterly bits of Thunderbirds filming, with many scenes cutting seamlessly between someone's hand picking something up, and then the puppet character holding it; and there's a brilliant moment when one of the robbers slides through the hole they have cut in the wall on an overhead cable. (I was straining to see - did they lock the puppet in place, and shove him through? Or was the hole in the wall actually open at the top to allow for the strings?)
I couldn't help but compare and contrast with the most recent episode of Doctor Who, shown exactly 40 years later, which also had a Christmassy theme. And to my delight, right at the very end, Brains pulls the same trick as the Doctor does at the end of The Runaway Bride - he makes it snow!
Checking up on the net to finish this post, I discovered that this was actually the last ever episode broadcast of the original Thunderbirds series. Well, unlike some, they went out on a high.