I with the rest of you Lamia was a filler episode, but i still found it enjoyable.
AC is right (as per ) the atmosphere in this episode was creepy, all the time there was this underlying feeling that something bad was about to happen. It was nice to give the knights center stage even if they did spend most of the episode being really nasty to both Merlin and each other! It was nice to see Arthur being unlike his father and sending help to distant villages, plus i loved having Guinevere doing something other than carrying a jug! I was pleased that Morgana had nothing to do with Lamia, it made a nice change!
Overall a dark and sinister episode, a good filler