Hrolf Kraki's Saga by Poul Anderson falls into the latter camp. It's a terrific little novel (260 pages in paperback) that moves with the speed of lightning and hits with the impact of Thor's hammer. As I said in a past post about Anderson (see my review of The Broken Sword), he's an author that seems to be largely forgotten these days, and when his name is mentioned it's usually for his prolific career as a science fiction writer, or for Three Hearts and Three Lions. But Anderson loved the Viking Sagas too. While arguably a better book, The Broken Sword is Anderson's creation; Hrolf Kraki's Saga is a retelling of the life and times of an actual Danish king. From the foreward by Lin Carter:
He was a real man, he really lived; he was the greatest of the Kings of the Danes and his court was glittering and fabulous, like that of Arthur at Camelot; there gathered the foremost heroes and warriors, the champions of their age--Bjarki, who held the charmed longsword Lovi; Svipdag, the slayer of berserkers; young Hjalti, who owned the magic sword Goldhilt.
But the old myths and tales of Hrolf Kraki are scattered and piecemeal. Anderson brings them all together in Hrolf Kraki's Saga (he calls it a 'reconstruction'), spinning a wonderful, epic tale in the process. It's a tale that's not for the faint of heart, as Anderson admits in his own foreward: