What are some of the characteristics Beowulf lacks?
Beowulf is clearly the story of an epic hero--Beowulf. He is, in nearly every way, the stuff of which kings are made. He is brave and selfless and truthful and honorable. The one area in which epic heroes often fail is the area of pride. Even in that area, though, Beowulf is generally not guilty. The one obvious flaw I see in him throughout this work is his rashness. He was in a swimming match for days, fighting off sea monsters and attempting to win the race and show himself victorious. He hears of Grendel's marauding ways, and he gathers men to go fight that battle. He hears that Grendel fights without weapons, so he plans to fight without weapons. Grendel's mother comes to retrieve her son's torn limb, and Beowulf follows her to the bottom of the ocean. Later, after reigning as king for fifty years, he rashly goes in to fight the dragon on his own--an act which costs him his life, as you know. This rashness may be considered pride or arrogance, as was attempting to show himself to be a man of unmatched valor; however, none of those acts really harmed others, and were, in fact, beneficial to entire communities of people.
Beowulf was a man who knew his own strengths and was not afraid to test himself, albeit often rashly. So, the qualities he might be lacking include cooperation, teamwork, discernment, and calm deliberation.