There are comments in this thread who take the position that it's a good, interesting, innovative movie but that the trailer can't do it justice and the core of what makes the movie good can't even be discussed without spoiling the movie itself. That's consistent with what I've heard from friends.

And the professional reviews seem to track the cult classic formula: mixed reviews but a handful of good ones, including those that point out that this movie isn't for everyone. Which is unusual for its budget, but isn't that unusual for an Iñárritu film.