I'm sure it's not the worst but I felt like the adaptation of Watership Down changed the tone/message compared to the book. Now granted the infamous violence is present in the book (though seeing it is more visceral than reading about it). But in the book there's a nice story at the end where Hazel is injured (iirc) and is taken in by a little girl and her parents who take care of him while he recovers before releasing him back to the wild (which only adds to his legend, of course).

Removing this bit, the only positive interaction with a human, makes the message feel more like, "Humans are bastards and inherently anethma to the natural world, which is also a brutal war of all against all even down to the cutest softest creatures." It just makes you feel bad, whereas the book might make you feel bad at times but it also offers an example of what you can do right. It's kind of a pet peeve when a work with environmentalist themes falls into that line of "Humans are the problem and there's nothing you can do but feel bad about it."