EP 1 - USS Callister was fun to watch only due to the context that they've put it into (original Star Trek), but the idea was already chewed up in White Christmas episode. I'm surprised they're thinking of spin-offing this one, there have much better episode in there catalogue.
EP 2 - Ark Angel had a interesting starting idea, but somehow they didn't done good job about detailing it. The plot is somewhat predictable, but I wouldn't call it a bad episode. Jodie Foster directing this one was certainly a surprise.
EP 3 - Crocodile was the first episode this season that felt like a true Black Mirror. Nothing too mind twisting or too much technology based, but it captioned the spirit of the series in it's psychologicaly claustrophobic athmosphere. You really expect twist as the episode progresses but the fact that it just kept going makes it real and shocking. One thumb up for this one.
EP 4 - Hang the DJ was praised a lot, but I must say it dissapointed me. I really expected that the core of the episode will be something revolutionising, but in the end it was just another love story, told in a different way.
EP 5 - Metalhead was a complete dissapointent. If it was a stand alone movie or something else I would say it was good. But in the context of the series it had nothing that all the previous episodes had: episode ended and you have nothing left to say/think about.
EP 6 - Black Museum was the best in this season. I really hoped that they'll make a episode like this in the next season but somewhere through the episode you could see the conclusion and just knew that couldn't happen. Nevertheless, the 2 stories portrayed by the protagonist had typical BM recipe for a great episode: technology based, ethnicly question, psychologically twisted and with no happy ending.