A lot of words can be used to describe this show. Some good, some not good. All in all, though, it's well intentioned but it's trying hard to do too many things at once: it's a mystery, it's a romance, it's a family break-up story, it's a crime drama.... It just doesn't really do any of them quite right. And although the actors are quite competent, especially the lead actor who plays Caleb, they all have to muddle through some bizarre plot twists and clunky dialog. And, without giving much away, the ending is not satisfactory -- then you find out that there's a whole other season: to explain what they didn't explain in the first season?
Maybe the real pleasure in this is the language -- the show is in Welsh, and listening to the words and rhythms of what the English language might have been like if its history hadn't involved so many conquerors is intriguing. Maybe just not quite intriguing enough.
Update: Just watched half of the second season, which might be the strangest show ever -- because nothing happens, despite numerous moments that seem to foreshadow some actual action. Instead, each long episode is empty of anything outside of slightly surreal conversation, some quite subpar acting, and hints that a plot might develop. It doesn't.