It’s easy to criticize long-running sci-fi series for losing their way after a few seasons. The initial spark might fade; ridiculous plot twists might emerge; the whole thing might end with a painful hand-wave of logic.

But let’s not forget that these hit TV series, and the expectations assigned by their fans, all start with some incredible coincidences. How often do we see the right cast, writers, directors, and out-there concept come together in a watchable, memorable series? And what about when such a series jumps on a seemingly familiar sci-fi trope, yet still digs up new ideas?