If you compare this movie to the Lem's novel there are a lot of differences. But don't compare them. The novel and movie have their own lives. I personally prefer movie. Tarkovsky is going beyond the limits described by Lem. It is not only the problem of Solaris planet and the relationship between main heroes. Tarkovsky reminds everybody that the origin of our problem is us. And all kind of the most important life keys you can find inside yourselves. The great Swedish director Ingemar Bergman said, that Tarkovsky is in the "room" where I just started to knock. You should see this movie if you want to know what is real you and what you really want. The movie is not the answer, but it is the step to your new understanding of your life.
Review of Solaris
