I have always understood that everyone agrees that he is one of the greatest sci-fi writers ever. His writing and philosophy has depth and he understood the future would be interaction between the society and technology.
Maybe he is underrated in the sense that while he is considered a great, many of his writings are still relatively unknown.
His nonfiction is also remarkable (Golem XIV is technically sci-fi, but it's so philosophically heavy that it can be seen as philosophical work).
* https://en.wikipedia.org/wiki/Summa_Technologiae
* https://en.wikipedia.org/wiki/Golem_XIV
'The Philosophy of Chance' has not been translated to English.
http://english.lem.pl/faq#P.K.Dick
Unless you consider it flattery that he told the FBI that "Lem is probably a composite committee rather than an individual".
But the lack of respect was not mutual!
Stanislaw Lem: Philip K. Dick: A Visionary Among the Charlatans
- Some Humans fear the AIs (pretty standard Frankenstein situation) and conspire against them
- The conspirators are eliminated as a threat, the narrator tells us they believe Annie did this because Golem would have done something subtle to avoid alerting humans whereas Annie simply considered the conspirators a nuisance and nothing above that - IIRC we're likened to insects, swatted away and, when they persist, crushed.
- With the AIs gone humans go on as if nothing happened, seemingly learning nothing from it at all
All of Imaginary Magnitude and A Perfect Vacuum are awesome in my opinion (I have read them only in translation)