Solaris by Tarkovsky is not uncriticizable, in the sense that "yes, it could have done what it tried to do better".

But a lot of what makes Tarkovsky's film sometimes bombastic is also what makes it work.

Solaris is ultimately about encountering something that you don't understand. The ppl studying it have theories, and draw conclusions, but its nature is ultimately a mystery that resists investigation.

Edit: so much so that essentially it's just a mirror (as mentioned)...the theories people have expose much about their own thoughts and preferences but don't seem to be getting any closer to understanding it...

The film is pretty obviously constructed to make you really appreciate the experience of interacting with the incomprehensible, by being deliberately obtuse and devoid of explanation.

Watching the film is as close as most of us might come to being stuck alone on a spacestation dealing with a high mystery; it's long, uncomfortable, wearying, and ultimately unsatisfying, as you don't come away from it with anything resembling a sense of closure...you end up knowing perhaps less than you came in with.

On the one hand, this makes it a crap movie in some ways: you never find out what 'the answer' is (what is solaris? why is it doing this?) or even a comfortable sense of the end (what happens to kris?). On the other hand, if the point of the film was not so much to tell a story as to communicate an experience, then many of the drawbacks and flaws can be seen as working towards that goal.

Contrast with say the monoliths from 2001: there's some kind of 'mystery' in the sense of 'who built them, how do they work', etc., but that's a very shallow mystery; it's understood / hinted at / explained (in the books, at least) almost exactly that they're artifacts that look for conscious life or the possibility of it, and then give it 'forward nudges' as needed.

So there's still a small mystery: 'who, exactly, built these things? how, exactly, do they work?' but for supposedly incomprehensibly advanced artifacts constructed by incomprehensibly advanced beings the reader walks away comprehending almost everything...

You have to decide upfront: is a film something that tells a story, or is it something that provides an experience...assessment will vary depending your choice there.