Firstly, reading all the previous reviews, bear in mind that this series was filmed in the mid-1970s and shot on 16mm film. For this reason film grain is far more obvious on the Blu-Ray version than on the DVDs I had previously. I bought this to replace the DVDs which were part of a faulty batch of BBC releases, the two layers separated rendering the discs unplayable. I'd already made copies of them before they deteriorated beyond recovery, but this looked interesting so I picked it up.
The discs appear to be fresh telecine transfers from the original 16mm films. They are presented in the original 4:3 aspect, as although 16mm film can give a 16:9 aspect it requires some vertical cropping and the shots would have been framed for 4:3 safe aspect. It therefore made sense to crop the transfer horizontally to 4:3, as anything in the edges of the frame would have been irrelevant anyway.
Bearing in mind the age of the material it really does look stunning. Yes, the sound is mono as NICAM hadn't been invented then, but it is presented in a lossless format. Yes, there's a lot of film grain, but this would have been there on the original DVDs, you just couldn't see it.
I've watched this on a 51" full HD plasma TV and it looks stunning. Is it worth replacing perfectly good DVDs with Blu-Rays? Questionable. But given that my DVD set was pretty much unplayable, yes, it was worth it.
Highly recommended if you either don't already have the DVDs, or if your DVD versions have become damaged. Or if, like myself, you've still got the original VHS versions that you recorded off the BBC in the late 1970s!