My first introduction to this story was, like many others, through Steven Spielberg's adaptation. For me, the hauntingly beautiful "Suo Gan" that serves as that movie's de facto theme song perfectly captures the fragile yet enduring beauty of humanity that Spielberg so successfully captures in his movie version. The movie abounds with poignant moments of hope, warmth, and exhilaration amongst the great struggles that befall Jim and his band of acquaintances. I enjoyed the movie, and Jim's story and haunting memory of Suo Gan made a lasting impression.
Years later, I encountered the original story--J.G. Ballard's novel that served as Spielberg's inspiration. Just as the newsreels and magazines that tell of the war fascinate Jim in the book because they describe a war so different than the one he knows, so does Spielberg's movie tell a different tale from Ballard's book. The events are by and large the same, but the tone of the story, the horrors experienced by Jim, and the lessons and impressions instilled by the novel are on a different order of magnitude from the movie. I enjoyed the movie on its own merits, but I imagine the order in which you encounter them colors your impression--for people like me who saw the movie first, it was easy to appreciate the movie, and then be blown away by the power of the book. For those who read the book first, I would imagine the movie would be a disappointing, sanitized version of the original work.
The novel overpowers the reader from start to finish by Ballard's stark account of Jim's survival against all odds, in conditions stacked heavily against him. Death, betrayal, illness, and hunger surround Jim and yet somehow he always managed to survive because he never despairs, never gives up, always keeps his wits about him, and as he himself explains, because he "takes nothing for granted." The world of WWII Shanghai strips humanity to its bare, naked, ugly core. Growing up in this environment, Jim becomes a remarkably complex character in spite of (or perhaps because of) his young age. Jim is intelligent, naive, loyal, callous, hopeful, curious, delusional, and yet oddly lucid--all at the same time. The image of flight is strong throughout the story, as a form of escape, and in some ways the only vestige of childhood granted to this boy as he goes through a life full of cruel ironies--first, the inability despite repeated attempts to surrender to an enemy that he needs infinitely more than they need him; then, the odd realization that this "enemy" is his greatest protector and in many instances, friend; finally, that even with the war over he is in greater danger and further from his parents than ever. War, peace, friend, foe, cause, effect, even the distinction between life and death ... these cease to have meaning for Jim. Finally, Jim is saved in an almost deus ex machina fashion by the heroic Dr. Ransome, a man whose selfless actions mildly amuse and baffle Jim, who cannot quite understand this brand of humanity which is quite different from the one he learned through his own experiences. Ransome's life is one that takes certain things for granted. Jim has not been afforded this luxury.
Jim's reunion with his parents is another, critical difference between the movie and the book. The "happily-ever after" ending in the movie is filled with hope and relief. Jim and his parents don't recognize each other at first. Then they do. This symbolizes that the war is finally over for Jim, now he can go back to a normal life. The End. In the book, however, the ending is much more nuanced. Despite returning "home" to Shanghai, Jim's home will forever be Lunghua in the novel version. Normalcy will never be a suburban life in England, for Jim it is wartime Shanghai. The odds of Jim being able to live what most of us would call a "normal life" are practically zero ... after all, he has just experienced a lifetime of events more "real" and vivid than "normal life" could ever be; the war never ends for Jim. Seeing the far-from-normal life Ballard himself has lead, and the fiction he has written, one realizes that even though "Jim" and "J.G. Ballard" may not be the same person (one crucial difference--Ballard is never separated from his parents), Ballard is still the adult that Jim would have grown up to be. It is this honest and uncompromising portrayal of Jim as a true tragic hero that separates the book from the movie, and makes this book one of the truly great accounts of surviving a brutal war that knows and shows no mercy.