There's also a great documentary on Stanislaw Lem. It's in Polish, but with English subtitles. https://www.youtube.com/watch?v=9wQq4aKldaw
Lem himself talks about the movie a bit there too, around the 24th minute. He didn't seem fond of Tarkowsky's religiousness and the impact it had on the movie.
Timestamped link: https://www.youtube.com/watch?v=9wQq4aKldaw&t=1434
My impression was similar — the movie seems to be a free retelling and doesn't reflect the book well.
It's interesting that Tarkowsky himself didn't like the movie either.
Authors are a bit too involved emotionally to judge movies that are based on their books though. It reveals to them that the interpretation that readers make of their books or their interest in it may not be what the author intended.