There is some argument among scholars as to whether the author came up with the Beowulf story himself, or was putting on paper epic tales which had previously been told orally. This certainly seems possible, as the adventures take place in Scandinavia, rather than in England, where the author was writing. From various barrows and other ancient ruins which have been excavated, it also appears that many of the characters in "Beowulf" were historical figures- King Hygelac, for example. And the Geats, Beowulf's people, were an actual tribe living in what is now part of Sweden.
Though the translation I read was good, the style is, of course, very old, but I didn't find it hard to understand. What I did find a bit difficult was keeping track of all the characters- there are a lot of them. This is especially true when the story is occasionally interrupted to reference and explain an event from the past involving a completely different cast of characters. No doubt these names would have meant something to the original readers- or hearers- but my knowledge of Scandinavian history and legend is virtually nil. Fortunately, the book included a list of characters and their relationships which I could flip to whenever I lost track of who was who.