Actually, I never really understand that is the book trying to tell a story, give a message or simply trying to glorify the heroes........what we can call the plot, is nice enough considering the time it supposedly was written in, but nothing very impressive, the message is old as the mountains, and the glorification of the heroes can be termed as exaggeration.
For example, Odysseus, who is nothing more than a minor charecter in Illiad, and does not seem to rise to much importance within the book's scope (unless we assume that there were some parts lost over time) has a full sequel about him.
Not that I am saying I don't like it, the books are excellent reading; I love the part where Diomed fights the Gods, I even find those long descriptions of the battle lines, Achillies' lament and all interesting. But what could have been the original point of writing such a book?