Everything you ever learned from Arthurian legend is being twisted and turned, but in a fun way.
Colin Morgan as Merlin
Bradley James as Prince Arthur
Richard Wilson as Gaius
Anthony Head as Uther Pendragon
Angel Coulby as Guinevere (Gwen)
Katie McGrath as Morgana
John Hurt as the voice of the The Great Dragon
So what's so different?
First of all Camelot has been established by Uther, and he's still alive and Arthur is a brat. Magic has been banned in Camelot and those found casting spells get their heads lobbed off. Quite fun.
Secondly, Guinevere (or Gwen) is just a servant. The personal servant of Morgana. We all remember Morgana as the evil witch. She's nice and likable.
You'll see many faces pop up, such as Lancelot, a young child by the name of Mordred, Geoffrey of Monmouth. Many more in the second season.
Did I mention they have a dragon?
Only one word of warning. I know many people will watch the first two episodes and just go 'meh'. Keep watching, it gets better.