Tarkovsky made films about what he cared about and what interested him. His Solaris wasn't really meant to be about Lem's book, just as his Stalker isn't about Roadside Picnic. Those books simply offer a setting where he could explore his own ideas.

Exactly. It’s a long time since I have seen Solaris, but I remember it as a film about human deficiencies, and especially the feeling of guilt, greatly amplified by the encounter with some “superior consciousness”. For me that’s a very interesting topic, very good angle, even if very different from what’s in the book.

I don't know, this might be the actual reason... or it's just that he couldn't really put the book into film. It's very difficult to do so, some may say it's just impossible since the mediums are so different. But your answer has been used before by people defending this or that director, and sometimes it just seems like a cop out, "Oh, he didn't really care about the book".

P.S. Sorry if I sound a bit harsh. Not my intention.

Can I attempt to clarify the perceived intention of Tarkovsky with his novel adaptation? I wouldn't frame the films as evidence that he didn't care about the source material or what it attempted to say. Rather, it seems to me that these films are his responses to the novels, or at least meditations on what the novels said to Tarkovsky.

Another factor is that film and literature are very different languages, and aiming for a 1:1 translation can often result in a work that is missing pieces that were only communicable in the original. If we acknowledge that any given novel will have aspects of it that are un-filmable (interior monologue, relative time dilation, for simple examples), then it is the job of the director to re-create the spirit of those aspects while making them work for his media. As a result, the director cannot help but inject his own views and thoughts into the work. Nobody embodies this more strongly to me than Tarkovsky, with Kubrick as a close second. In fact, King's own attempt (shudder) at filming The Shining may prove this point all by itself; it's apparent that King doesn't understand the medium he was attempting to use.

I disagree with you on that. While I haven't seen Soderbergh's version (I am too much in love with T's) I think the idea of communication is deeply embedded: he's saying, we can't communicate with ourselves - how could we possibly communicate with an alien non-humanoid entity? I think he makes that really clear.

For anyone who hasn't watched his films: take an afternoon you have nothing to do and slow down. It's not a passive experience and you need to relax to take it all in. Amazing stuff that I can't imagine not having in my life, plus all the great directors he influenced. Him and Bergman == life of film.