It seems to me that Gerald Durrell is underrated as a writer; so many other writers are far less deserving yet have praised heaped on them (classic writers especially - Hemm... *cough*). So I wonder why this is? Perhaps it has something to do with the subject matter Durrell chose - wry humour, animals, travel. Perhaps if he decided to write about a world war that he was not really involved in then he would be a great? My opinion is that, ultimately, Durrell is a down to earth, non pretentious writer with the discipline for expression. I think this is why I admire his work.
There are a bunch of underrated writers, and there could be a bunch of reasons why they aren't more famous. One reason could be that writing isn't their primary job (as in Durrell's case). Another could be that their questionable political affiliations overshadowed their writing talent. Etc.
I love Gerald Durrell- I agree that he is underrated, and he is definitely one of my favourites. I love his whole Corfu trilogy, though My Family and Other Animals would have to be my favourite. I think the fact he is underrated is probably to do with the fact that he writes about such a specific topic (mostly on his childhood in Corfu, with the focus being on animals), in addition to the fact that it wasn't his main profession. To be honest, if my parents hadn't bought me My Family and Other Animals when I was a kid, I highly doubt I ever would have read his work if someone recommended it to me.
I loved Birds, Beasts & Relatives. It was to me like the Adrian Mole for nature enthusiasts. He hit a nerve as I was a nature loving kid, but I can see how that would have limited appeal now, since kids spend their childhoods these days watching movies and engaging in electronic amusements.