This film was positively brutal. I can't say I liked it but it is not because the actors are bad. They are all excellent. The director really likes to hit you over the head with the allusions to red being blood on the hands of Tilda Swinton's character. This device got annoying after the first 10 minutes of the film.
The beginning half-hour is so disjointed because of the bouncing between time periods. I understood that the point was to illustrate the whirlwind of despair and loss and guilt that Tilda Swinton's character is experiencing but it was overdone.
This film is exhausting because there is no resolution and no redemption. To the very end Kevin denies his mother any reason for the horrific acts he commits.
You could argue that in real life violence never has a justification and therefore this movie simply mirrors life. I would rather have seen this movie tell me something more. If I want to hear about horrific violence all I need to do is turn on the news. I would have liked this movie to have given something more than a hopeless and bleak resolution.