Which cancelled show was left on the most anticipated cliffhanger?

Having just binged three seasons of Designated Survivor for the third time, I don't think there's been any other cancelled show that I want an extra season of more. The ending as it stands is just enough to bring an ounce of closure to the show, but they also set plenty of groundwork, character development and a cliffhanger to make me need those extra few hours.

Interested to see what other shows we should have gotten one more season of