Okay, I'm giving it a 4.5 really. I take off half a star for the following: 

*Lofty word choice - it may just be me, but his word choice slowed me down a LOT. And not like, big words, but really unusual words that don't help the story at all. There WERE unusual words that were pertinent during the time period and so, yes, I don't mind looking those up, rock on. But LOADS of other words I feel like nobody would use over and over and it helps nothing. Maybe I'm just grouchy, but it seemed arrogant-ish.
* So many characters that were hard to keep up with. I had to go back a few times and say, "wait, what?"

HOWEVER.

This is THRILLING and I found myself holding my breath while I read sometimes. Ridiculously good story (of course it is, it's Blake Crouch). The back and forth in time were aligned perfectly and many times I found myself shivering because the cold was described so perfectly. So much of it believable and unbelievable at the same time.