Overall, I kind of felt this episode was of the suck, because there hasn't been enough build up for Arthur's actions to completely ring true, Morgause was sprung on us from nowhere, and once again there was too much plot in too short a space. Also, Merlin as comic relief is wearing so, so thin.
But there were three things that totally redeemed it for me.
1. The scene between Arthur and Uther before the fight was really well acted. Tony Head is just amazing. The fight was pretty awesome, too.
2. Merlin's tearful little face when Arthur declared he had been shown once again that magic is evil - thanks to Merlin. Oh wow. I always think Colin does a much better job with subtler depictions of emotion like that than he does when he's being shouty. His shouty just doesn't have much of an emotional impact (because his voice is weirdly monotone --- is this a result of having to use an accent other than his own?) His tearful little face really does.
3. The Uther and Merlin scene. Once again, Tony Head bringing it. (I sometimes think this show should be called Uther. He steals every scene he's in.)
In contrast to many episodes of Merlin, the conclusion was actually considerably better than the rest of the episode. Usually we get good set ups with no follow through, but just to keep us on our toes we got bad set up, facinating follow through.
And next week looks completely unrelated again. I would say my main problem with this show is that the writers can't decide if it's a series or a serial. It isn't episodic enough to truly be an out-and-out series, what with Morgana's continuing storyline and the Nimueh storyline from last series --- you have to have seen something before to pick it up. But it doesn't have close to enough continuity to be a serial.