Series 4 is thoroughly enjoyable - if you're not too concerned with accuracy and the portrayal of events and key figures from the 1980s from a 2020 viewpoint.
Gillian Anderson's portrayal of Thatcher is a bit hit and miss. She has the walk and mannerisms spot on but the voice a little too low and husky and the stoop is mystifying.
Corran as Diana is very good, as are the rest of the established ensemble.
The sumptuous production values sometimes have to stand in for lapses in the script - but otherwise it's still glorious viewing.