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.
Complete Monster: The evil scientist Thatcher Redmond originally comes across as just a Smug Snake with a nihilistic worldview, but only pages after we meet him, we find out that he killed his love child to avoid paying child support. He drips with contempt for humanity, and when faced with the incredibly deadly Henders life forms, he sees the opportunity to advance his plans. He leaves his fellow scientists to die on Henders' Island, does everything he can to eliminate the intelligent and gentle Hendropods, and indisputably crosses the Moral Event Horizon when he releases five Henders Rats onto the ship with the intention of unleashing them on an unprepared humanity. The guy's as close to an Omnicidal Maniac as a normal human villain can get.
Designated Hero: Geoffrey Binswanger. Despite spending most of the story at a university mocking the existence of the island where the other main characters endure great dangers and suffer the loss of many friends, he is clearly set up as a hero who gets the girl despite only showing up in the third act and doing almost nothing heroic.
Moral Event Horizon: Thatcher arguably crosses it right off the bat when we find out how he set up the death of his own son to remove the inconvenience of a love child. However, if this doesn't count, he steps over once again when he deliberately releases Henders Rats onto the ship, hoping that they'll lead to the extinction of humanity.
In Pandemonium, Kuzu is a far more sympathetic villain than Thatcher Redmond ever was, but by the time he's become convinced humanity needs to be wiped out with Henders fauna so he and his fellow Sels can inherit the Earth, he's well over the line of no return.