I loved this episode!
I really felt for Morgana -- knowing that something's "wrong" with her and not only having no one to tell, but realizing that if she did tell, she'd be killed by someone who claims to love her. And Merlin was so heroic trying to understand and help her -- even if his actions did result in the arrests of all those people and the death of DruidLeader!Colin Salmon. Mordred was creepy and wonderful -- I can't wait to see more of him. I also liked that Arthur is projecting all of his feelings about his forbidden desires for Gwen onto Merlin (although I did see a lot of real chemistry between Merlin and Morgana).
This ep showed that even more than with Arthur, Merlin has to protect and guide Morgana. It's too bad (but ultimately for the best, I recognize) that he didn't show his hand at this point and reveal that he too is magical. At the same time, I think this may end up being how it went down with Clark and Lex in the Smallville universe -- Morgana will eventually sense that something's different about him as well, and his continued lies will erode her trust in him. I like the character of Morgana so much -- she's regal, beautiful, strong, and kind -- and I'll hate to see her descent into evil (although it should be interesting).
But yeah, great stuff. Colin Morgan looked great during this episode -- not too skinny in the face. I just wish they didn't waste the wonderful Colin Salmon by having his character killed off. It would have been great if he could come back.