The Iliad and Beowulf both celebrate warriors and a warrior culture. Valor comes from performing heroic deeds on the battlefield, as does earthly immortality. Achilles, for example, is given the choice between a short life of heroic glory and a long life of domestic happiness, and he chooses the former. Beowulf, too, hopes to be remembered for his deeds of valor.
These are both masculine, patriarchal cultures, where male physical strength is valued and bonding among male warriors occurs. Warriors are expected to sacrifice themselves for the larger community. Hector, for example, would rather stay at home with his wife and young son than go to war but knows where his duty lies. Beowulf also comes to Heorot out of a sense of duty. Hrothgar believes it is because he once helped Beowulf's father, but we are led to believe it goes deeper than that: Beowulf feels obligated to protect civilization itself by protecting the mead hall.
A difference between Beowulf and the Iliad involves scope. Beowulf is concerned with the protection of the mead hall, which is posited as the center of civilization and all it represents—warmth, safety, food, companionship—is pitted against the grim marshes and moors of nature from whence monsters arise.
In the Iliad, men fight against other men, not monsters, and the civilization they are charged to protect is larger than the mead hall. As the shield of Achilles shows, the Greeks are fighting to protect an entire society that includes outdoor areas such as pastures and fields. In Beowulf, humankind is united in a struggle against the malevolent forces of nature that monsters represents.
Finally, women are more fully incorporated into the world described in the Iliad while they play almost no role at all in Beowulf. Gods and goddesses, too, play an ever-present, participatory role in the Iliad's drama.