I'm not what you would call a "Doctor Who fan," but we've been watching all of the recent series on our Roku Netflix box lately. There are a lot of pretty cheesy episodes, but I've generally enjoyed most of them.
However, the other night we watched an episode entitled "Blink," from season/series 3 (episode 10), which I believe originally aired in 2007. Holy crap that was a good episode. I mean, not a "good -- you know, for Doctor Who" type of good, but a seriously fantastic hour of television. The story is great, the writing is great, the villains are great. It's scary. It's clever.