These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Man After Man: An Anthropology of the Future
Inferred Holocaust: While not visually shown, after all the massive time and energy used to create these species, the last remnants of altered/evolved humans were abandoned on a somewhat dying Earth to die a slow and somewhat painful death by suffocating and starvation with no way to save themselves simply because they were not built with the general intelligence to do so. It can be considered somewhat of a Tear Jerker as well.
Nightmare Fuel: Mainly in the books' highly detailed illustrations of evolved and genetically altered human/animal species. One notable species is called the Tic; a human with an organic version of the cybernetic cradle the Hiteks get around in. They're completely dessicated humanoids whose organs are constantly failing, so they replaced them with artificially grown organs. It was simply more convenient to grow entire organic exoskeletons. They are not a separate species from the Hitek, their technology is simply more advanced. In addition, many of the creatures appear as if someone needs to call in Master Chief and have the whole planet nuked from orbit.
It also ends with the descendants of Humanity returning to Earth, which is populated by the various descendents of genetically modified humans. So what do they do? They annihilate the vast majority of Earth's ecosystem, with the remaining creatures engineered to fit their needs, including a gargantuan"meat creature" with no recognizable head or limbs. In the end, they destroy all surface life on Earth except for the descendents of the humans engineered to live in the ocean, which colonize the deepest parts of the ocean. It is implied that those deep-sea dwelling "humans" will eventually recolonize Earth's surface.