The ending is a punch in the stomach. It leaves you with a strong bitter taste in your mouth. It might be the right feeling to have because mental illness is bad, it's mean and it's immensely difficult. But the ending also has a sort of Sixth Sense feeling and it suddenly transforms a nicely done movie, very delicate, to a movie that seems to be more interested in shocking you with an unexpected ending.
In any case, I recommend watching the movie.