"USS Callister" embodies everything that is great about Black Mirror: disturbing, original, weird, thought-provoking. And they even threw in a comedic factor. It was so good.
I also loved "Hang the DJ" but felt it was a little obvious they were trying to recreate the magic of "San Junipero."
So far I've heard the most negative reviews for "Metalhead" aka Robot Dogs but I really liked the horror factor. When that thing ran out of the factory the first time I screamed.
I did not like the finale. I liked the stories within the finale more. I thought that first story about the doctor could have been its own episode. Imagine if they made a dark, serial-killer, American Psycho kind of thing? Oh well.
LASTLY:
check out all of the easter eggs and connections you probably never noticed.