When the Russian film master Andrei Tarkovsky adapted Solaris, he jettisoned almost all of Lem’s philosophizing. (Like Stanley Kubrick, whose 2001: A Space Odyssey he considered cold and sterile, Tarkovsky took a cavalier attitude toward rendering the work of others.) In some ways, his film is richer for it: where Lem executed a thought experiment about alien contact, Tarkovsky moves the focus away from the ocean planet and onto the people overcome in its wake. Most of the characters remain sketchy in Lem’s depiction, but Tarkovsky gives them personalities and human histories.
Tarkovsky felt like he failed with Solaris because it retained an SF flavor (which he did succeed in stripping from Stalker), but I’m glad that he wasn’t able to rid it of its genre trappings. As it is, Tarkovsky’s Solaris is SF as it should be, concerned with ideas and fleshed-out characters.