Man I totally did not expect this movie to go down the way it did. It makes me like it that much more since it was different from what I expected.
Essentially there is a battle between God and the Devil and some of the Devil's spawn think they are sick when actually, they are just part demon.
There were a ton of creepy jump scares that obviously caught me by surprise.
I love all the subtle symbolism that alluded to the fact that the Devil was around.
Other than that, I really had no idea till towards the end what was going on with Eli and his auto-immune condition.