Love triangles certainly aren't new, and "Guinevere" does absolutely nothing we haven't seen everywhere else. Guinevere is set to be married but Arthur is drawn to her, they consummate their relationship, but Guinevere is married to Leontes at the end of the episode. The main problem is that this dominates the episode, leaving little time to explore areas which are, you know, actually interesting, and Arthur spends the entire episode not doing anything relating to his duty.
What makes the episode worth watching, however, is the continuing development of Merlin, an enigma who seems the opposite of a benevolent mentor. Instead, we see him trying to control Arthur, and in his interactions with Morgan, his magic seems rather dark as well.
Score: 7.8/10
