The cast and set are different every time, but one theme I found recurring was that each episode was extremely haunting, and it definitely gets the viewer thinking about what could be if the world was just a little bit different. I don't think Black Mirror will appeal to everyone because some themes are a slightly uncomfortable especially in the pilot episode. So far the actors that have been cast have done an amazing job, and the writers have managed to make some far fetched ideas seem graspable. Basically this series is unlike anything else on TV and for that it gets a big thumbs up from me.
I don't want to write any spoilers, but what I will say is this if you want a drama with dark twist or a series that is completely Original make it Black Mirror.