I think it'sgreat, and it's not at all my typical 'thing'. I dont like period dramas and I'm pretty much a republican! It's really interesting though, and really well acted (made me fall in love with Matt Smith all over again). Season 2 gets a bit quiet in terms of the writing, but it's really worth watching the whole three/four series. Except the Aberfan episode, which I still haven't been able to watch. I know the story too well, it's just too heartbreaking.
I've even got my husband into it, he loves the historical aspect. He never knew, for example, that Edward VIII had been in contact with Hitler, and was somewhat supportive of his intentions (at least, in terms of power). Obviously, they have taken some liberties with the history, some is exaggerated or changed for dramatic effect. The crux of the history remains though. I'm genuinely fascinated with how they're going to play the Diana story both this season and next.
And if nothing else convinces people to watch it, the actress who plays Anne in season 3 is absolutely bloody marvellous, its worth a watch just for her few scenes. Really, they need a spin off of just Anne in her youth being a sarky cow to everyone in sight.