I'd said at the time that it seemed a very difficult book to adapt, since it concerns magic in the "real world" of 19th century England, conjuring up such things as stampeding sand horses on the shores of the English Channel in a battle against Bonaparte. Also, much of the fun of the book is that it's written almost like a history book on magic of the era, complete with countless footnotes referencing many supposed existing books about magic at the time, complete with stories from them about "real" events. It's also long -- somewhat over 1,000 pages.
Overall, I thought they did a strong job with the adaptation. A great deal had to be cut, even for a seven-part mini-series, so I had the sense that people who hadn't read the book might be a little lost in parts. The other day, I spoke with a friend who had been watching, and I asked if he was at all confused by things. He said that, in fact, he was -- though he still was enjoying it quite a lot. Just a bit bewildered by things...including not knowing enough about the main antagonist and being a bit uncertain about his background and who he quite was.
Cinematically, it was all wonderfully done, and they handled the magic effects fluidly (which is no small thing) and extremely well. My one quibble was what I'll describe as -- so as not to give anything away -- "the darkness." It's a critical part of the story at one point, and impactfully written and sustained. In the mini-series, they set it up reasonably well...but don't really maintain it well, I didn't think.
The performances were generally quite good and true to the book, lead by Bertie Carvel and Eddie Marsan (as Strange and Norell respectively). The one thing I didn't agree with was the portrayal for Mr. Norrell. He begins the book as the odd-ish hero, though his shy anti-social side and wariness about his student Jonathan Strange -- and his over-protectiveness about magic and its risks -- cause him to become somewhat of an adversary to Strange. I thought in the TV adaptation they emphasized Mr. Norell's ego and distrust of others too much, making him come across as more selfish to the point of almost seeming at times the story's antagonist, when he's really well-meaning in his concerns, but deeply misguided in too many of his actions. That's not the actor's fault, but clearly the direction the production chose to take.
Overall, I think they did a commendable job for a difficult undertaking.
It's interesting that they called this the "season final." The conclusion certainly does lend itself to a continuation -- but there's no second novel. The author Susannah Clarke is said to be working on one, but that was announced in 2004. There's no indication of when it might be finished, let alone published. And any adaptation and production would add a lot of time on to that. So, I wouldn't think a "Season Two" is at all imminent.