30 Days of Doctor Who, Day 2: What’s your favorite episode (and why)?
"Professor, I’m glad you’ve got an absolute definition of life in the universe, but perhaps the universe has got ideas of its own, hmm?" - The Doctor
There’s multiple reasons why I love this episode. The monster is of the unseen/incomprehensible variety that, to me, is much scarier than any CG creation. Its existence calls into question the common assumption that alien life must be of a certain kind (hence my favorite quote, above). The Doctor, cut off from Donna and the TARDIS, has only his wits and his sonic screwdriver to defend himself, and yet it’s not until the humans turn against him that he gets well and truly freaked out. The monster is scary, yes, but it’s the worst impulses of the human race that are the real danger.
Also, Colin Morgan. Nuff said.