Pretty awful casting of the family. However, I liked the actors portraying the Al Fayeds, and thought that they were spot on. Similarly, Edward Viii and Wallis. My favourite episode was the one with the brilliant Bahamian valet that featured all of these. The Diana stuff on the other hand, was tedious and I feel as if I’ve seen it all so many times.
I enjoyed the Penny storyline and I thought that Jonny Lee Miller’s John Major was nuanced. I liked Lesley Manville’s subtle portrayal of Margaret’s sadness and regret. Marmaduke Hussey was great.
The royals didn’t get the cut-glass accent right in the way that Claire Foyle and Josh O’Connor (for example) did. They sounded middle-class and occasionally would throw in a “vair” or a “heppy”.
IMO Dominic West was too sexy as Charles, not spoilt/peevish enough.
Jonathan Pryce got Philip’s candid stare down to a tee, but otherwise didn’t capture his ascerbic nature. He didn’t look polished enough, either. Prince Phillip was immaculate.
The actress playing the Queen Mother was too tall and too light. The QM was short, and famously gluttonous, with a pudgy face. There was a reason why Mrs Simpson and her spiteful smart set called her “the fat Scottish cook” behind her back.
As for the OP’s question…an unpopular opinion, but I would have kept the original cast and “aged” them with makeup, wigs and padding, as they did so well in Heimat and The Forsyte Saga many years ago.