Bought the DVD set at Wal-Mart last year as a Christmas present for myself. Best investment ever. The Video Diaries are hilarious and I have seen them so many times, it's insane. Colin Morgan plays Merlin, and honestly, there is no one else that can pack invest so much emotion into a character as he does. His prince, Arthur Pendragon is played by Bradley James. It's a character that suits Bradley well, with his smile and his prattitude.
Of course, I don't actually watch the show for it's scriptwork, or the plot, because they're a little weak, what with being a show focused mainly as a family-attraction, but oh, it is so much more than that. The underlying UST between Merlin and Arthur is undeniable, questionably the sole reason for it's giant fanbase. You can't watch this show without feeling a sort of want for their relation, however one sees it. It's there, it's tangible, and it's great casting, great chemistry, and excellent television.
The supporting characters are as follow: Gwen (soon to be Queen Guinevere) is played by Angel Coulby. Having seen Angel Coulby in few other things before, I'd like to say she adapts to the role of Arthur's future queen quite easily, and interestingly enough, the romance between her and Arthur is downplayed, second to Arthur's relationship with Merlin, as it should be.
Morgana (LeFay) is played by the beautiful Katie McGrath. She is the best female character/actress on this show. Her storyline begins somewhere in the middle of season 1 and is worked up until the most recent season, involving her historical significance, and a few other spoilers, I won't mention. Either way, McGrath's emotions are paralleled with Merlin's seeing as she has things to hide as well, and every episode that takes her on as its main character are one of the best ones.
Next we have the older, more distinguished actors like, Richard Wilson, as Gauis, playing Merlin's mentor. He and Morgan share the more comedic scenes, and while they get old, they are still funny after the sixth or seventh viewing. It's funny seeing Wilson with a wig, I guess.
And Anthony Stewart Head, who plays a prominent role as King Uther Pendragon, Arthur's father. It is he that has forbidden magic throughout the land of Camelot, and he plays his tyrant role to a T, which is funny considering Anthony Head is about the sweetest thing since candy. It is interesting to see his scenes with Arthur. (Bradley James is a huge fan of Buffy, and references his intimidation of Anthony Head in the Video Diaries on the last disc. In which you can also see Anthony Head playing on his pink Nintendo DS.)
Suffice it to say, the cast are excellent, the plots could use some work. Less filler episodes, less comedy, more action, more magic, more slash. Perhaps if Johnny Capps spent more time working on Merlin and Arthur's relationship, rather than the random Arthurian Legend insert of the week, there'd be a considerable chance at the BAFTAS. Either way, Arthur and Merlin, they're golden. Their banter is one to look forward to. And their deep, intense stares at one another, suggest another kind of depth to their relationship, and it makes up for anything the series lacks.