So overall I liked it, probably because at heart I'm an evil Sheppard/Teyla shipper (yeah, I like Teyla; she hasn't been used to her potential but I think it's definitely there), but also for other reasons. It was a great episode for Joe -- he got to show some nice range and the effect was definitely eerie. He also had interesting character moments with Lizzie, Teyla and, to a lesser degree, Ronon. The plot was something of a combination of Bane, Upgrades and Broca Divide... somewhat derivative, but then again, what isn't? It worked for me.
That said, there's always stuff I can nitpick on *g*
Number one gripe with the episode was how Lizzie behaved. Let's start with Caldwell. Okay, maybe he was trying to "take Sheppard's place", but I really doubt that it was anything personal. Caldwell's never been shown to have a bone against Shep like Everett did at the beginning. I would think that it's just part of being in the military... being ready and able to step in for a comrade when they're out of commission, whether it be for a day or a week or the long term. It's not in his personality, I think, to sit on his hands and 'keep someone's seat warm', which was what Lizzie expected him to do. He tried to reach out to her and she pushed him away, which can be partly excused for her concern for Shep, but she's also plenty bitchy to him at the end when it really isn't called for.
Next, her behavior when it came to Sheppard... oy. I was cussing at the TV (or would have been, if there hadn't been a 10 year old present) when, twice, she went into Shep's quarters and closed the door between her and the armed guards. WTF, woman? And do we really need to ask the mutating man how he's feeling every few minutes?
I know some people are going to excuse this behavior or use it as proof that omglizzielovesheppardandwantstomakebabie
I think the writers need to be careful when it comes to Liz. I can see how she would be a tricky character to write, the same way that Janeway seemed beyond the grasp of most of the Voyager writers... striking that balance between savvy leader and a nurturing figure. There are times when she's a little too on for her own good (like with Caldwell) and times when... what's the phrase, Sel?... her brains dribble out her ears.
seldear has some good thoughts on this over in her journal, too. I agree with her about the importance of showing some character interaction between characters other than Shep/McKay and Shep/Liz... something along the lines of Ronon and Teyla in Duet. I want to see Shep and Carson, and Teyla and Weir, or Weir and Dex, or Dex and McKay (besides them just snarking at each other).