The Trojan War is a fascinating event, at once both myth and understood as historical in nature. To the Greeks, there was no question of the fact that it had occurred-- even Thucydides accepts it as fact. They believed it had happened. Perhaps not to the scale of the poem, but a war had been waged between the Greeks and the Trojans. The poem was treated as historical record for a very, very long time, as much as it was a view into legend and later, the myths of the gods, and a work of art and literature.
Homer's Iliad (perhaps not quite as long as it is today, and certainly not exactly as it was written) was an oral recitation before it ever made it to paper--or scrolls, but we can still see in its language the devices used by a bard or story teller to complete the meter of the lines and allow the poet to remember what comes next. The poem is full of repetition. Phrases, even entire passages are reiterated. Some of these things are identifying characteristics such as "white-armed goddess Hera" and "bright-eyed Athena" and others are ritual, such as the description of how offerings and sacrifices were made to the gods. That the repetition is preserved in the poem as it was written down is fascinating, and it's a veritable gold mine of an example for writers who may be interested in trying to adapt their written work into something that could be sold on iTunes to the world of people attached to their mp3 players. These devices could serve us just as well as they did ancient bards.
The other beautiful (and problematic) thing about The Iliad is the smorgasbord of customs! Because it comes from an oral tradition, and the poem was refined by each teller for his time, using this catalog of phrases, they could and did insert new, more modern ones, as time went on, adding them to the archaic phrases and customs already in place. This means that looking at the Iliad for daily customs for a particular time is probably not going to give you a good picture of any specific time and place, but rather, an overview of customs for an extensive period in history from the Bronze Age into the Iron Age, thrown back on the Trojan war as an historical event.
In my personal opinion, the a lot of the value of The Iliad is not its preservation of an historical event, but in the preservation of the gods and their characters. Sure, it also gives us a look at how war was glorified and the ideas of the Greek culture in that regard, but it's hardly of the same historical significance in regard to the actual event it transcribes as, say, Thucydides' History of the Peloponnesian War. From the epics of Homer we are given a lot of information about the society and culture as a whole, especially its reverence for the gods that were worshipped. But its those gods that give the story mythological and legendary proportion. The gods involving themselves in mortal affairs, from Athena sweeping down to stay Achilles hand from striking at Agamemnon to Achilles own immortal heritage, and Helen's.
It's not unlike the Old Testament, when Prophets walked the earth and the voice of God boomed from the heavens. The destruction of Troy as a vendetta by Hera and Athena isn't that far different (though much more mercurial) than God's own destruction of cities and peoples that displeased Him. But the story does more than just capture these moments between gods and men, and goes so far as to show us the infighting and strife that must have been ongoing between Zeus and his wife and his entire family. We are given the understanding of the gods as a disagreeing family under the rule but not entirely submissive to, their patriarch.
We are also given to understand that a great war such as the one waged against Ilium was more than just mortal rage and lust for plunder, but set in motion by forces beyond mortal understanding and control. Ordained and encouraged by the gods, so to speak. A theme which I find fascinating to the extreme.