I love Beowulf for two reasons. First, it is the story of a truly bad-ass hero, a take-no-prisoners slayer of monsters (and their mothers) and even dragons, who became a king in his own right. He's the template for epic warriors from Conan to Aragorn, the toughest, most fearless bastard in an era of tough fearless bastards. This is the guy who sees a trail of bones leading into a dark lair and charges ahead while other guys remember pressing appointments elsewhere. Yeah, I know that Gardner's 1971 novel Grendel takes a sympathetic view of the main antagonist, using the creature as a vehicle to explore nihilism and ostracism, but I ain't buying (nor, by the way, did I buy the weird animated-but-not-really 2007 version with Anthony Hopkins as Hrothgar and Angelina Jolie as clothing-optional Grendel's mother. Icky.). This is one hero I'll take straight up.
The second reason Beowulf is so intriguing is that it continues, more than a thousand years after its writing, to stir controversy and academic debate. It's set down in Old English, but is it Scandinavian in origin or Irish? Was it influenced by the epics of Virgil, or even Homer? How many of the Christian references are original and how many added later by pious scribes? Tolkien himself lectured and wrote extensively on the subject, on both historical and linguistic questions. You have to love a story that is still compelling and meaningful a millennia later, and provokes ongoing contention among historians. And you have to love Beowulf himself, a dude who carves out his own kingdom by defeating a savage monster, rules for a half-century, and then dies while beating another. They don't make them like that any more.