At a press screening for the fantasy drama's fifth series, Julian Murphy admitted that he is now "horrified" by how certain scenes were realised.
"If we look back at the first and second series, we're pretty horrified at the way we executed it - genuinely - 'cause we can do things so much better now," he explained. "The look and feel of the show is richer and more detailed [now], and that had a real effect on how you experience it as a viewer. We're quite proud of that shift."
Murphy also suggested that the BBC show's storytelling has evolved alongside its visuals.
"In terms of character, we've gone from telling relatively simplistic stories-of-the-week to [episodes that are] a little bit richer, [with] a little bit more psychology, a little bit more depth," he said.
"I think these shows can take that - if you look at a good Hollywood PG family film, you get all of that."
Merlin star Colin Morgan recently indicated that the fifth series will see "a maturing" of the show's characters and themes. The show returns to BBC One next month.
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Watch a trailer for Merlin series five below: