As Lem explains in the introduction, the fake book review (and fake acceptance lecture), as particularly exemplified by Borges's book reviews, is a micro-genre suited for intellectual jokes - for ideas which need more than a tweet, but can't be written out unironically or in full as articles/books. (If dry academic humor is not your thing, you probably already know from reading descriptions that you should not read this book, so I can address fellow aficionados.)

One way to fail in this rather abstract micro-genre is to tell too much - since this is a genre where more detail can make it worse the same way that a horror movie can be worse when it shows too much and the horror collapses into irony & camp when you see the rubber monster. Lem's own fakes succeed when they maintain this distance from the subject matter; this is why "Robinsonade", "Gruppenführer Louis XVI", "A Perfect Vacuum", "You", "De Impossibilitate Vitae and, De Impossibilitate Prognoscendi", and "Non Serviam" fail, as they try to be the works they purport to describe (particularly "A Perfect Vacuum" and "Non Serviam"), but of course neither Lem nor anyone else could write them for lack of the required exceptional talent & knowledge.

Still, that leaves half the volume as successes, interesting and amusing.

"Gigamesh" takes Finnegan's Wake into the Wikipedia age, describing a mobster story with improbable allusive density where a single item requires several pages of lists of things it is an allusion to; while it's easy enough for Lem to merely tell us that such a chapter in Gigamesh is an encoded work of classical music which comments on the events of the chapter, Lem goes one better by showing us at least 26 interpretations or allusions he is able to contrive for the word 'Gigamesh'.

"Sexplosion" is a satire of technologizing sex which takes a left turn, leaving us in not so much a dystopia but a weirdtopia where food assumes the role played by sex, down to the pornography and moral hysteria (a satire particularly pointed these days by the extent to which all sorts of sexual deviancies have been normalized but the moralizing of food seems to have hardly ever been stronger).

"Pericalypse" is a modest proposal to treat the inexhaustible emission of human culture as not an asset but info-pollution, to be discouraged because every book written obscures further the best books, a viewpoint with which I have some sympathy myself.

"Idiot" proposes a psychological horror novel (somewhat similar to "Robinsonade") in which the parents of a retarded child convince themselves he is intelligent, and perhaps he is and has been murdering and rearranging his life as convenient; like most horror, in the end humans are the real monsters, as Lem has described little but 'facilitated communication' after all.

"U-Write-It" is another parody like "Sexplosion", but where "Sexplosion" criticized human tendencies towards over-moralizing everything, "U-Write-It" criticizes apathy & disinterest toward fine literature by the general population in describing the commercial failure of an attempt of an Oulipo-like company to sell its kits for splicing together classic novels into new fanfictions - the moral being, of course, that most humans are not interested in or even capable of such disrespect. (One has to wonder what Lem would have made of FanFiction.net; is the glass half full or half empty?)

"Odysseus of Ithaca" offers an inversion and image that seems like it should have been in Calvino's Invisible Cities: searchers convinced that the greatest wisdom by the greatest geniuses, truly original thoughts, would be ignored and not understood as comprehensible by the general population ('if a lion could speak, we would not understand him') and so to find treasures, they must search through sewers and insane asylums and trash cans. ("Odysseus" could have been combined nicely with "Pericalypse", I think.)

"Being Inc" is an update on Borges's "The Lottery in Babylon", with more computers; what I loved most about this one was two throwaway lines: "Antitrust legislation in the U.S.A. forbids monopolies; consequently Being Inc. is not the only life arranger. There are its great competitors, Hedonica and the Truelife Corporation."

The story "Culture as Mistake" has as its core an interesting argument: that 'culture' can only refer to everything which is not useful or backed up by reality, and so, in the strictest and most concrete sense, all of culture is lies and mistakes.

And finally, the piece Lem calls the best, and I would have to agree, the "A New Cosmology". Here Lem offers up an explanation for the Great Silence: all our knowledge predicts countless alien civilizations but we observe not the slightest trace (here nothing has changed, as modern astronomy vindicates Lem's assumptions of the commonness of planets and entire absence of signals or anomalies), and this is because the aliens have become so advanced that they have become indistinguishable from nature; but here, where most speculation idiotically stops, showing that the author has not thought in the slightest bit about resource limits or competition or exponential growth or the likelihood of all aliens being consistently the same way over billions of years without the slightest deviation, Lem keeps going, suggesting that the laws of physics themselves have already been molded by the most advanced aliens in a previous multiverse as a solution to an intractable conflict in which different bubbles of physics in the multiverse try to expand (erasing and eating other bubbles), where the solution hit upon by all parties independently is to fix a single common set of physics, and that we do not see the original universe but a successor, a stabler successor with physics strategically chosen to limit the ability of any alien civilization to expand or tinker with the laws (especially the lightspeed limit), where the existing alien civilizations continue to remain silent & hidden as they strategically continue to tweak physics like the value of certain constants while wishing to avoid tipping off competitors. This is a theory of the Great Silence which is far from idiotic and quite interesting as a hard SF premise. (It still doesn't work, though. While the multiverse part is unfalsifiable, the explanation for our current universe still makes no sense as lightspeed is not that much of a barrier and we can easily imagine expansionist strategies which make more sense; eg when it only takes a few million years to colonize a galaxy, if you're worried about competition, why not put Von Neumann probes around every planet to kill competitors in the womb, so to speak?)