Er, he let her go because she helped save everybody, including him, as she'd pointed out. Plus he seemed quite fond of her.
I didn't think this episode was too bad.
Superficially, it was very nice to look at with some decent effects and good cinematography. The story was okay, although the bad guys weren't really that scary or anything. I'm not sure why, since the idea of aliens that eat everything till all that's left is dust sounds good on paper.
Michelle Ryan's character was pretty well played and fairly interesting, one of the best companions for a while imo. Way better than Kylie or Donna. I normally can't stand Lee Evans, but he wasn't completely unbearable in this ep, even with the pointless Welsh accent.
The flying bus thing... just seemed like RTD over cooking the plot as usual. Also, the effects were all over the place with those shots. Some looked realistic, then others looked awful.
Telepath lady was pointless really.. they could've found a better way to give a sense of foreboding. I don't mind people on Who having "a sense" since there's a precedent for it, but it is overly convenient when they turn up.
Oh and I noticed the bus had adverts for a phone company called Neon? Am I over eager to spot easter eggs, or will they turn up in the last special as some company that the Daleks use to control everyone? They have a stable network!