It's hard to rate this film because it has so many different levels on which such a rating might be based, both dark and light. To begin with, there's a lot of graphic sex (how do actors do these scenes as mere 'simulations'?) and even more nudity. If that's to your taste, you'll love this film. On another level, it's a pretty searing portrait of the ruthless Soviet crushing of the so-called Prague Spring and the subsequent imposition on the Czechs of their always oppressive totalitarian regime. At times, it can be quite comedic, at others painfully tragic and sad - especially at the end. There are also elements that defy credence, specifically that the character of Tomasz (Day-Lewis) appears to possess the mesmeric power of inducing women to remove all their clothes by simply saying, "Take off your clothes" (tip to guys: try this line at your peril). I confess to not having read Kundera's book, on which this film is putatively based, so I don't know how faithful to that novel it might be. The principle actors - Day-Lewis, Juliet Binoche, Lena Olin - are all superb in these difficult roles and Day-Lewis makes it difficult not to envy his character's easy sexual success, but this is a very complex and emotionally challenging story, not just a sexual romp. In fact, even the sex - which tends to dominate the film - is often compromised by painful emptiness and futility, much like real as opposed to movie life. This is not a happy story and these are definitely not happy people. The fact that the two main characters choose to return from a life of freedom in the West to the dismal, soul-crushing tyranny of life in Soviet subjugated Czechoslovakia is presumably the basis for the title; that they ultimately find the lightness of being free unbearable and are thus compelled to return to slavery - the classic Stockholm syndrome - and there they ultimately die.