From supernatural jaw-droppers to time travel twists, there have been a whole lot of sci-fi TV cliffhangers left dangling over the years.

The reason? On average, around half of the shows on TV will be canceled at the end of any given season — which means plenty of perfectly awesome sci-fi shows never made it into their potential prime. Looking back into the annals of sci-fi television history, you could make a list that numbers into the dozens digging into shows that left fans hanging, forever asking what could've been.

Instead, I've narrowed it down to six that really grind my gears. First, some qualifiers: Not all of these shows were great (looking at you, ABC's V reboot), but their cliffhangers were. We're looking to drill down into cliffhangers that left a show with such a great set-up that it's heartbreaking the creative teams never got a chance to pursue them. Which is why a deep cut like ABC's Miracles makes the list, and not something like the muddled (but more popular) Revolution on NBC.

Okay? Here we go ...