The Guardian has an article on this:
Even a lavish period BBC drama such as I, Claudius feels a bit low-rent by today's televisual standards. The acting is formidable indeed but technically, it's very static and staged. There are long, "unblinking eye" camera shots, occasionally trundling in for close-ups in moments of high drama, with very few cuts
I disagree with the Guardian that pre-1980s TV is poor, or even 'low rent'. It is just operating to different implicit standards. Something happened in the 80s so that TV stopped being a type of theatre and became a type of cinema. We don't say theatre is static and staged, with low-quality sets, because we don't expect a stage production to be like a film. It has different virtues. As they say here 'the acting is formidable indeed'. It's the acting and scripts that were (sometimes) very good in old telly.
I wish that critics and viewers could be persuaded once again to see TV (well, some TV at least) as a type of theatre. I think that would get us away from a fixation on verisimilitude, and would allow lower budgets, which might make TV executives more open to formal experimentation and moral challenge.