Despite its title, Irreversible is told entirely in reverse. A violent act of revenge preceded by a vicious rape and the events that led up to it. This movie is not for the faint of heart because it is unflinching in its documentation of said brutalities. It is a disquieting tale of things that happen beyond our control and it reaches us because we feel so helpless. We realize that it could be us, no matter how different our lives are, and there is nothing we can do to stop it. Its realistic depiction is aided by single-takes. Its use of music effectively ratchets up the tension and speeds up your pulse. I love a scene near the end, where the two people who become tangled up in violence and rape are instead entwined in each other; evil is replaced by love.
But there is so much to hate about this movie. From beginning to pretentious, baffling, experimental end, the camera rotates and swirls around to a fever pitch. Your stomach literally churns; I could not imagine seeing this in a theater, especially not an IMAX. The camerawork feels like a gimmick to physically make you as sick as the disturbing events do at a mental level later on. There was a decidedly unnecessary and gratuitous amount of nudity, sex, and violence in this movie; some of it was essential, but as a whole it became almost exploitative, as if its extensive presence had the sole purpose of shocking the audience.

Despite my rating, I cannot make a blanket recommendation of this movie to anyone. You have to know what to expect and have to be ready to take it all in. It is hard to digest, but not without merit.
IMDb link: http://imdb.com/title/tt0290673/