So in this one the Doctor decides to take Martha to the future, to New Earth, back to New New New New New New New New New New New New New New York. It makes me smile every time he does that. But this time they're in the Under City, and everyone is going onto the Motorway (British for freeway, for those of you Americans) and never coming back. People are going 6 miles in every 10 years or so. Martha is kidnapped by a couple who wants to go to the fast lane, which requires at least three passengers. But the fast lane is home to malicious creatures of legend.
So the Doctor freaks out trying to save Martha, because he promised to keep her safe. She sort of whines in the car, but does credit the Doctor with the ability to save her, and is ecstatic when he does, indeed, save her. Probably my favorite part about this episode (apart from David Tennant as the Doctor, which is always my favorite part) was the different cars they had, and how the Doctor was dropping into all of them. My particular favorite was the guy with the bubble wrap.
The Face of Bo (sp?) kind of scares me honestly. It's just sort of weird, and then he only communicates telepathically despite having a huge freaking mouth. And the cat lady was a little too devoted to him, almost to the point of creepiness. And I think the Doctor played down the fact that the Face of Bo (spoiler!) told him that he was not alone. I'm not quite sure why; I mean, of all people, the Doctor should be the one most willing to believe that there is at least one more Timelord in the universe. Maybe he did it for Martha's sake. I'm not sure. But his planet sounds freaking awesome! It's really too bad that we couldn't have seen it...ah well. My imagination probably does it better justice.
So in conclusion, good, interesting episode, but I'm still just not a fan of Martha. It'll probably go the way of Christopher Eccleston, where I'm just not into her until the last two episodes, and then she's gone forever. But whatever. I'll live.