Just finished watching it and loved it. I've now been learning about the real Franklin expedition and now think that if it was just told as a survival story as opposed to a horror story that it would have been just as gripping. Not all survival stories end in survival!
The decades spent looking for them also make a good story, one of the ships that were part of the search was HMS Resolute which suffered a similar fate to the Terror and Erebus. However, the Resolute was found by an American whaling ship and returned to Queen Victoria. As an offering of thanks, timbers from the ship were made into a desk which now sits in the Oval Office!
The Erebus was finally found in 2014 and the Terror in 2016 - mind blowing!