Cabin Fever is one of my favourite plots, ever (love reaches back to the first season CSI episode where I've learned of this phenomenon), and the realisation here was perfect. The right amount of paranoia, creepiness, and danger.
The creature was freakin' scary, and the reactions from all the passengers were priceless. And I do think this was the least funny episode of the season, in fact, it wasn't really funny at all.
It was scary and sad, and the people were just as much of the monsters as the monster itself. The fear of the Other, turned into the fear of the-enemy-within, believeable, and worrying.
And then, my favourite thing of it all, was taking the running gag of the series (companion trying to speak in the language of the place/time, Doctor going 'don't do that') into something sad, too.
I love, that the high tension was kept up by the performances, and by the strength of the characters. No special effects, no monsters, no bumps-out-of-nowhere, no creepy camera work and changing faces. Just wide eyes, and repetitive voice.
And the trailer looks fun, too.