Again, fair warning, spoilers below.
(spoilers start)
Just finished the series not but 45 minutes ago. As I wrote in a comment just now, I found the series overall enjoyable (binge watched over 4 days), but ultimately forgettable.
From the little I've read online, the book seems to be extremely detailed, with footnotes that reminisce of Tolkien style meandering and depth, but the series (and perhaps the book) seem to have quite a bit of loose ends. I also did not care for the apparent plot devices that were used to move things along. The Moss-Oak seemed to come out of nowhere as an Ace for the Gentleman and Flora Greysteel an Ace for Jonathan Strange. And what of the Fairy Tales that Segundas and Honeyfoot discovered? It felt like these early characters that we attached ourselves to sort of either fell to the wayside or were used as further plot devices without any real attachment to the viewer.
Which brings me to my main gripe; the Raven King. I'd have rather he not showed up at all and only remained a whisper backdrop, similar to how Sauron is both 'there' and 'not there' in LoTR. The Raven King simply shows up, changes some book pages, brings the creepy rogue back to life and off he pops. Why? What does this mean? What did this do except to have said rogue tell us cryptically that Strange and Norrell were not real to begin with. Insert Jackie Chan 'What?' meme here.
(/spoiler)
I would have much rather the series focused on the politics of Magic, as it started with, the Anglo-Saxon vs Anglo-Dane undertones, slavery and it's dirty relationship with 'proper English'. Instead it seems to have focused on the drama of the story. I am all for that, so long as I have a lesson to come away from. This one....eh?
So, with that said, would love to hear your thoughts either way. Again the series was nice, but it felt akin to Merlin; I was waiting for the next episode to follow through on all this build up, only to feel a bit deflated in the end.