Okay, first off, everyone's taste in movies is sujective. Everyone claiming this movie is "horrible" and "unwatchable" or any variation thereof: first of all, calm down. It wasn't that bad. I figured out the big secret about 2/3 of the way into it but it didn't ruin the reveal for me in any way. Also, it's a horror movie; they never end super great for the protagonist(s) so stop complaining about the ending. I thought it was appropriate for the genre and not at all surprising.
With that said ...
It was just intriguing enough to keep me awake (I watched this movie after midnight last night), just scary enough but not SO scary that I wanted to turn it off. I thought the acting was serviceable although the protagonist was a little whiny at times. I chalk that up to his being a teenager and they can be pretty whiny.
I can't speak for the sound design or score because I was watching this in bed with my sleeping wife next to me so I had it turned down with the subtitles on. I may watch it again with the volume up and I'll update my review at that time.
The creature design was disturbing and frightening. I actually held my breath the first time it came on screen. There's not a lot of gore but I found the person-on-person violence pretty believable and sometimes hard to watch.
The pacing felt a little slow in the beginning but it picked up once our protagonist finds out he's not alone. It doesn't run away from you, though, and the I thought the pace was decent once things started happening.
Overall, I really enjoyed this movie. It's not one of those movies that makes you think about much or forces you to examine heavy themes or to introspect. If you want one of those, I would recommend Lost Child, which you can also find here.