I liked what one reviewer said about the movie. He said that Macnee and Rigg should have been cast in it, damn their ages. Not a bad idea, really. They could have been the equivalent of "Mother" and "Father", and had two new young leads doing the rough stuff. Of course getting Rigg to do it would have been a major hurtle.
It is best left in the '60s. It's too bad there wasn't a film of it made back then. Nearly all movies made from TV series are disappointing.