He avoids what I call the 'People in Fursuits' syndrome, which is to write 'animal ficiton' simply personifying the animals as acting like humans. Adams has the characters acting on realistic concerns and non-human perspectives, translated into human language. I can't even really think of any other animal characters in any fiction that springs to mind as much as Adams'. King has some in his stuff, like Oy in DT or the dog in Insomnia, both those are just memorable portrayals from a human perspective.