Really? Unlike Lost, BSG and Twin Peaks, Carnivāle was pretty fully plotted from the get-go. Sure, the story isn't completely wrapped up,
Well, that's an understatement. I would rather say 'ends on massively infuriating cliffhanger.'
To me, "cliffhanger" means that something big is just about
to happen/get started. See: Marty stuck in 1955 again at the end of BttF II
, "The Best of Both Worlds, Part I". But Carnivāle
was always intended to be a six-season trilogy of three two-season parts, and, given the tone of the finale's last scenes, I expect there would have been a lot more build-up to the next
big event in the overall story. So sure, the epic was unfinished, but I wouldn't call the finale a cliffhanger per se