Solaris, the book, is one of the best sci-fi novels of all time. The recent movie didn't get close to conveying the idea behind it, neither visually nor story-wise. I watched the Russian movie (originally funded as a communist response to 2001: A Space Odissey, I heard) a long time ago, so I don't remember a lot of it.
A little bit of trivia: did you guys know that around the time when Solaris was published, lots of sci-fi fans from the west believed that the book (along all Stanislaw Lem books) had been written by a new computer the Soviets were developing? They thought it was a computer for a moon landing module, from the name "Lem"- Lunar Expedition Module. Well, Stanislaw was a real person in the end.