I watch a lot of horror/suspenseful films but honestly, this one left me baffled and wanting more, because, ironically, I don't know if I'd identify this film as horror. That being said, I think the best way to watch this movie is not to watch it from the perspective of a horror film and to go in knowing nothing about the movie. If you can do that, you'll probably enjoy the movie more than you would if you have the expectation of supernatural spooks and jumpscares.
As for semi-spoilers:
This film feels more like the beginning of an awesome superhero/supervillain franchise than a standalone horror movie. I would not at all be opposed to reading a comic book series or something related to Eli and his future because it really gives off this "twisted Percy Jackson" vibe, which I think would identify with a lot of those who love supernatural/mythological elements but are adults and want more adult-ish content. While I do admit that there are some strange things about the movie which make me hesitant to give it higher than a 4-star rating, personally, I really enjoyed the movie and would probably watch it again.