I've now watched the first two seasons of Black Mirror, as well as the Christmas episode.
Mostly, it's great stuff. Strong satire, great direction and acting. There's enough skill involved that egregiously soapy episodes like The Entire History of You wind up not feeling all that melodramatic in the end. And The Waldo Moment really is frightening in hindsight, isn't it? The episode itself is kind of a mess, but so portentous. Again, certain very strong aspects keep the whole thing from going off the rails.
The crown jewel of the series so far, however, is Fifteen Million Merits. What a monster of an episode that is. Right at the center is a bit of light, love and authenticity. Those are the stakes. What happens to it is what makes your stomach churn. There's so much attention that went into crafting every detail of the episode's aesthetic, from the score, to the avatars, to the interactive panels...it's like a cross between the Wii menu and Requiem for a Dream. It's a very absorbing episode and that goes a long way to making it so suffocatingly nightmarish. And I don't use that term lightly; it really gives off this helpless, sorrowful tone that's also frighteningly uncanny. I've had nightmares that felt exactly like watching this episode. It feels very real and plausible, but you don't want it to be.