Poul Anderson really was one of the greatest authors of speculative fiction. Many great authors can write swashbuckling heroic fantasy, or hard science fiction, but not many can write both with equal facility. Anderson was one of the few who could, possessing a degree in physics and a great depth of knowledge of Nordic mythology and ancient languages. "The Broken Sword" is one of his pure fantasy stories (and also one of his earlier novels), and draws heavily from northern and western European myth and legend. Anderson takes an interesting approach, postulating that the mythical creatures and deities of all cultures really existed, and sometimes interacted with each other. Thus, in this story, you see elves, trolls, dwarves, and other creatures from Nordic mythology, including some of the Norse gods, the Sidhe from Irish mythology, and even a lonely satyr from Graeco/Roman mythology -- a survivor of the supernatural creatures that followed Roman colonists into Britain centuries earlier. Even Christianity is present, acknowledged as a new and growing faith that is slowly, but inexorably driving out the others (the book is set in the era when Danish Viking armies were settling large parts of northern England during Anglo-Saxon times).
What's fantastic about the book is how well Anderson evokes the myths of that era. All the essential elements of Nordic epic myths are present: the human hero, of special origin, almost superhumanly mighty a warrior, and like virtually all such heroes, fated to meet a tragic and early end; elves, dwarves, giants, trolls and gods, often at war with each other, or at best, an uneasy and fragile peace; powerful curses which work slowly and subtly, but inexorably to bring about their ends; characters motivated by hatred and revenge, whose grievances are not wholly unjustified; even Odin, travelling secretly (and sometimes appearing openly) in the world of men, and manipulating people and events, just as he did in the Norse myths. It's all here, especially the grim and tragic mood that pervades Norse mythology, for the epic tales of Nordic mythology were nearly always tragic. It's amazing how well Anderson captures the spirit of the epic material from which he drew his inspiration. This is one of his most unique and interesting stories.