"[Homer] is rapid, plain and direct in thought and expression, plain and direct in substance, and noble."
Taking place in the tenth and final year of the Trojan War, the ILIAD opens with the anger of Achilles at the great king Agamemnon for taking away his favorite concubine (a spoil of war). Each man's pride is too much: Agamemnon refuses to give back the girl and Achilles refuses to continue fighting. Since Achilles is the Greeks' greatest warrior, the fortunes of the Trojans markedly improve while he famously sulks in his tent. But the Greeks fight on, and such heroes as Diomedes, Aias (Ajax) and Odysseus continue the fight to sack Troy as return the queen Helen to her husband Menelaos, King of Argos. Over the lengthy yet colorful descriptions of battle, they are driven back to their ships by the Trojans, led by their prince and greatest warrior, Hektor (brother of Paris, who has stolen Helen with the help of Aphrodite).
The ILIAD is really the story of Achilles, and is his tragedy. Once the danger of defeat seems imminent, Agamemnon offers to give the girl back and make amends (as long as Achilles realizes who's still boss) but Achilles remains caught up in his prideful wrath. He eventually returns to the fight and drives the Trojans back inside their own walls, but the price he pays is dear.
The ILIAD is also notable for its depiction of the gods. Far from being above it all, Athena, Ares and their immortal siblings get right down on the beach and take sides in the war. You might think that a battlefield is no place for the goddess of love, but don't worry, Aphrodite soon learns the same. The Greeks will suffer, but the greater powers of Mt. Olympos are behind them, effectively making their victory inevitable.
Since Lattimore was trying to get as close to the Greek as he could, his English translation is less poetic than those of Robert Fitzgerald or, I imagine, Robert Fagles (who is next on my list). But it does have its own stately rhythm that should hardly be inaccessible to the modern college student or adult. For high schoolers, though, I would recommend reading one of the other translators first, as the first time one reads Homer, it should be for the story. And what a story!
Reasonable people differ on translations. Having struggled through part of the original, and having read Lattimore, Fitzgerald, and a bit of Fagles, it is Lattimore who seems to capture best the vivid, occasionally gruesome, quality of the original along with its noble and transcendent aura.