Long story short: if you have seen any possession horror movie, like the Exorzist, you won't find anything new here - at least in the horror elements. Few paranormal activities, few / lame jump scares, some good reflection / shadow moments - but overall too few for a great horror movie. I'd skip it unless you're a die-hard ouji fan.
What is good and praised by other reviews, is the well done story of a teenage girl. You experience the day to day live and problems of the protagonist. That's great to get the audience involved, but I felt the movie was 85% of that and that's too much for a horror movie, where the "horror" itself falls short.
There were a lot of questionable things that didn't add much to the plot overall - what was the significance of the solar eclipse aside from the teacher's remarks early on? It supposedly aided the being to enter this world, but the movie never picked up on that aspect again later, rendering it a generic explanation of the events. And what's with that scene where time went backward as Veronica went forward and then that doppelganger appeared? It didn't have any meaning, it's just a generic "scary" scene that could have been added to any horror movie.