I first read this book aged about 13, in the Science Fiction Special No 28, borrowed from my town library. It introduced me to concepts and dilemmas that have informed my entire adult thoughts: This Book Changed My Life. Parts of the book are pure adventure, parts are an intelligent discussion on what rights we have as individuals, and what we owe others in return. Is it "from those according to what they have to those according to what they need" or "mine is what I can take and hold"? Philosophy as exciting sci-fi, if you will. Or possibly, exciting sci-fi as philosophy.
Sadly, after I had borrowed and read 'SFS No 28' about 12 times, it was loaned to Stafford Prison Library and then stolen by some criminal! It took me ten years to acquire a copy after looking in every second hand bookshop I entered. That was five years ago. Now this excellent book has finally been reprinted, a shiny new copy can be yours (or perhaps your thirteen year old nephew's?) in only ten seconds... what are you waiting for? ;-)