It's UK only. The BBC likes to keep their British programming a secret from us Americans (and other people around the world!) who want to watch new episodes of BBC shows. :(
I would watch this show solely to watch the guy who plays Arthur. Mmmm men in armour :D
But as it happens I like the show too. The dialogue is often pretty hackneyed, but the concept of the show is so good that I can get over some of the more cliched scenes between the characters. We're behind the Uk where I live, but I think it's definitely getting better as it goes on.
I agree with this ^^ I think that'll be very interesting
While I do love the style and concept behind Merlin, I don't actually watch the series -- whether that be because I don't have time, or I don't feel like it, I don't actually know.
However, the Griffin episode? Totally worth it. Hooray for the most amazing mythical creature and a great portrayal of it. ❤️
Edit: And for the record, it is being aired in a few other countries outside the UK.