I like that Cole, a mercernary survivor in a post-apocalyptic wasteland went into the past and saw the world as it used to be and gained more compassion and hope whilst Cassie goes into the bleak future, as a doctor who was living in a present where her earth wasn't wiped out by a plague, suddenly sees firsthand…

The reason Cole was stuck, as I understand, was because him using the serum so much had done something to his blood and was killing him. So they used the blood of a version of himself that had never been injected with the serum to "wash out" the bad blood (i'm sure this is Totally For Real Science) but in turn making…