I have heard Solaris refered to as being mind-changing before. What was it about Solaris that impacted you so much?
After first hearing about Solaris decades ago, I finally got around to reading it upon learning of his passing. I must have missed something because it didn't strike me as living up to its reputation.
I can see how the dry digressions (which I personally enjoyed) and lack of resolution could rub some readers the wrong way, but I found the philosophical questions it raised valuable, not to mention the mystery and human interest woven between it all. There are of course other works with this kind of thought experiment (like the movie Arrival and the short story it’s based on), but I find Lem’s pessimism refreshing.
The Solaris ocean is utterly alien to the point that the humans are unable to understand and communicate with it, despite it clearly possessing some form of intelligence. The alien isn't a mirror for the human reader. It also presents issues for science, since Solaris can't be understood, implying that science is limited by our being human. And that kind of mind-blowing.
This is the theme of all Lem's novels involving aliens: Planet Eden, Fiasco, Solaris, The Invincible and His Master's Voice. It's the opposite of our Western optimistic idea that we can face any challenge and solve any riddle, either thanks to a universality of scientific reasoning (such as in Greg Egan's novels) or because the aliens are nothing other than Americans or Nazis in rubber costumes (as in most SF blockbusters).
Then again, I have no idea what life might do trillions of years in the future, if there is any life around then. But if there is, I highly doubt it will be remotely human, so what difference would it make to us now?
He explores this in "Eden", "Solaris" and "Invincible". All three are highly recommended.