Sci Fi Fans! Tell us a specific show or if it's popular, an episode of a show that you are enamored with and why

I'll start: my personally favorite sci fi that that I wish more people knew about is Orphan Black. It features Tatiana Maslany really showing off her acting prowess. Basically, she plays a street rat who encounters an identical but well off version of herself who jumps in front of a train. In discovering this apparent twin's life, she realizes there's yet more of her and that they're being killed off.

The cast, both Tatiana and not-Tatiana, are really good at embodying their characters and the world is neat at showing something that could actually be happening under our noses this second.

Edit: here's a low spoiler example