If you really like this book then you must realize that you don't know what a good post-apocalyptic novel should work like. Ok, it achieved a cult status because it was one of the pioneering novels in the sub-genre of post-apocalyptic fiction. But the book is so far from the reality that one might guess that it is a cross between William Makepeace Thackeray's "Vanity Fair" and Pat Frank's "Alas, Babylon" (though "Alas, Babylon" came after "On The Beach").
True, there are some endearing as well as heart wrenching moments alike in the novel, but Nevil Shute's characters are just resigned to the fact that they are going to die and they never even try to take some measures to resist the radiation, no matter however futile they are. They don't even try to outrun it. The whole world just sits and wait for the radiation to kill it, as infuriatingly slowly as possible. Come on, basic animal instinct for survival is far greater than anything else.
One trivia for you if you have got an IQ of more than 50: What would you do if you knew that radiation is going to engulf your city after a few days? Well you would run in the opposite direction even if you knew for sure that that is only going to give you a few more days to live and nothing else. But even then, you would try. And if you don't, you don't deserve to live anyway.
There is so much wrong with this book that I can go on and on. But I will stop here. But personally, I don't think that this book deserves to be in the list with classic post-apocalyptic novels. Read "Alas, Babylon" instead.