I liked how us (the audience) were kept on edge when we couldn't really decipher what was real and what was not, since the narrative is generally played through the main character, a schizophrenic teenager with vivid hallucinations. However, I think the movie itself could have been more of a thriller. I like the scary aspects in thrillers, but there weren't very many in this movie.
Leading up to end of the movie was good; you had no clue what might happen since there were various possibilities. However, the ending was poorly executed. It was all too fast and left very little time to enjoy.
Overall, the movie is good and worth watching if you want a decent plot with a not-so-scary "thrill" aspect. If you're looking for more than that, I wouldn't waste your time.