I'm having mixed reactions to this ep. Not so much for the reasons I've seen many others state, i.e. that they reset the Merlin/Arthur relationship somewhat -- I figure that's in part to it being a season opener, and they have to restate the basic setup. No, the plot of someone tricking his way between two characters is not something I like, because I get squick-like reactions. First this is almost like partner betrayal, but also it comes uncomfortable close to my embarrassment squick, because I cringed for Arthur being duped when we realize that the guy is tricking him. So the first half was hard for me to watch.
But the second half was a lot more fun. I liked the action parts, and also how Gwen saved Arthur and he was awkward afterwards.
As a side note, what was Gaius saying around 19 minutes in, after he says to Merlin "Not everyone thinks you're an idiot"? It makes Merlin chuckle but I couldn't understand the dialog.