Read the German translation published by Goldmann back in the 70s. After Farmer's very avantgarde "Riders of the Purple Wage" in "Dangerous Visions", this seemed like a huge step down both in literary quality and in visionary content - 2/5. But 1-1.5 points might have been "lost in translation"...
The 5 stories:
1) "Prometheus" (same title in both languages) is a shockingly naive and old-fashioned account of first contact with an alien species and of a single human educating them, bringing them from their paleolithic starting point up quite a few tech levels. Mixed with some theological musings, as that human happens to be a monk. Besides the naivety of the whole setup, it's reasonably competently written, and as a 10-year-old I would have enjoyed it without reservations. But the other stories in the volume clearly make this an adult-oriented publication, and I can't take this simplistic story seriously on that level. Also, the human characters (main guy plus some support scientists in the background) act horribly random and unscientific. In the end, my only redeeming thought about this one is that Farmer might have written the English original as a parody, and the translator completely missed that point...?
2) "Programmierte Ausweglosigkeit" ("Down in the black gang") at least can be recognised as coming from the same experimental writer as "Purple Wage". A weird story about the whole universe being a "ship" run by some sort of psychic energy mechanics. The purposefully weird language has aged unfavourably in German, but that's a typical translation problem. More seriously, the narrative arc unfortunately is just not very interesting. But at least there's the interestingly weird idea.
3) "Die Gotteslästerer" ("The Blasphemers") is certainly the high point of the volume. An alien race with unconventional body plan, procreative and social structure. (Though the social structure actually seems implausibly similar to ours.) They're starting a large-scale space exploration program in a social minefield of clan traditions, religion and teenage ennui. Quite a bit gimmicky at the end, but a decent read.
4) "Außerhalb von Raum und Zeit" ("The Shadow of Space"): A faster-than-light spaceship accidentally leaves the universe and enters into some weird meta-space with non-existent or abstruse physical laws. A silly, but promising setup. But the story is crippled by flat characters, too much narrative randomness even when the premise is the absence of physical predictability, and blatant misogynism in the characterisation of the woman who's blamed for the accident.
5) "Eine Schüssel, größer als die Erde" ("A Bowl Bigger than Earth"): Obviously a Proto-Riverworld. A random guy dies and is resurrected in a strange world consisting entirely of an everything-made-out-of-brass city along a single river, peopled by resurrected humans turned into physically uniform sexless beings who are also suppressed into hyper-communist psychological and social uniformity by unseen entities. The setup was obviously fruitful, as it later led to the whole Riverworld franchise, but this first attempt is just a painfully underdeveloped thought experiment.