I've watched this series about 4 times, I just don't know what it is about it. It feels like home. The relationship between Merlin and Arthur is the most beautiful and funny I've seen on TV. I am very aware that the dialogues can feel a bit corny sometimes, especially in the first season, but it's just...endearing. The adventures are really fun, more so in the last seasons when the tone gets darker. Obviously the CGI isn't the best, and the show has its overdramatic moments, but it doesn't impact the quality significantly. Oh and the ending is not great and feels a bit rushed, which was a bit heartbreaking. It's not perfect but when you're this emotionally attached to a show it means it's pretty good.
Review of Merlin
