The only reason I'm sad this show was cancelled is due to seeing so much of Theo (and his body double) naked. I don't think we will ever get a movie/or show that Theo is in that calls for this much nakedness. I mean he was literally nude in most of the episodes.
As far as the show. I can see why it was cancelled. The story is essentially that a young girl meets a naked, mature, adult man (time traveller) in the woods. Guess what? They are also married. No matter how you describe that. It is creepy as hell and borderline pedophilla.
The show can also be difficult to follow with so many moving parts. I haven't read the book, but it seems from those who have read it. The book was always going to be too difficult to adapt properly anyway.
Finally, the show also should have had a different co-lead. Rose Leslie had ZERO chemistry with Theo and it severely impacted the show. She is awful in this.