Having never seen any of the series in question, I can only judge this film on it's own and not as a comparison. I found it interesting, particularly as an example of life in the '70's. The way that the 'islanders' were portrayed was pretty laughable as I'm sure anyone living off the coast of Cornwall would agree. This lot, regardless of their problems, were more like the Stepford Wives.
I agree with the point about the medical knowledge. I can't believe they thought that it was possible to reverse physical defects even in 1972. This does affect the credibility of the film but it's not a major problem.
It was an enjoyable way to spend an hour and a half though, not what I expected and I would definitely recommend it. However, I have to pick up on a point from an earlier reviewer - Ian Bannen was no spring chicken, granted, but Judy Geeson would have been 24 at the most. Therefore, your comments about them being middle aged were hardly fair. And a stirling job was done by both Bannen and Geeson.
And if anyone spots Pam St Clement, who is listed in the credits, please let me know!