I’ve been a huge fan of the Iliad and the Trojan War since I was a kid, so I was eager to see this. However, I couldn’t help taking notice of all the discrepancies from the literary tradition. I know the film was just a film, and that the literary tradition itself has little (if any) relation to historical reality… but if you would just indulge me for a moment as I pick out those discrepancies. Please note that I don’t mean all of these nitpicks as criticisms–some changes worked quite well, though some don’t–I just can’t help noticing them, in any case.
No gods: Most obvious difference from the literary tradition, with barely a reference to them at all (I think the temple of Apollo, and maybe a passing reference to Zeus, may be the only mention of the gods). Surprising that Athena, who played such a major role in the literary tradition, doesn’t even get a nod (not that I noticed, anyway).
Menelaus’s banquet: In the literary versions, Paris does go to Sparta as a Trojan envoy, but Hector doesn’t go with him. The movie also indicated that Paris had been visiting Helen every night during his visit, while in the literature she’s dragged away (although not entirely unwilling). The movie also went to great pains to villainize Menelaus–he’s loutish and ugly and very unsympathetic. I suppose that this makes it easier to understand why Helen would choose Paris, but Menelaus really isn’t that bad in literary depictions. Paris, on the other hand, was perfectly played by Orlando Bloom–a charismatic pretty-boy, but not much of a hand with a sword–just like the literary Paris.
Agamemnon raising the Greek/Achaen army: the movie invents the idea that Ag is intent on dominating the Aegean. Ag’s ulterior motives are absent in the literary tradition, but I think they work well in the film–while the idea that he’s just helping out his brother and defending his family’s honor works fine in the literature, for a modern movie it looks a bit silly. Giving Ag a more credible cause for war makes sense. As with Menelaus, the movie goes over the top in making Ag totally villainous and conniving. This portrayal is easier to accept, since Ag was kind of a jerk in the literature, too–maybe more of a jerk, as his sacrifice of Iphigenia shows–though the movie makes him to be more of a boor than is probably necessary.
Odysseus recruiting Achilles: in the literature, Achilles is still a teenager, living with his mom (Thesis, a sea-nymph–the movie alludes to her original status by having her wading in the waters picking sea shells–I thought this was a nice touch). Thetis doesn’t want Achilles to go to war (she’s always been over-protective in that sense–remember her dunking the baby Achilles in the River Styx to give him near-immortality), so she’s dressed him up as a girl. Odysseus is able to identify Achilles when the boy, forgetting his disguise, reaches for a sword instead of jewellery (when Odysseus offers both as gifts). A rather sexist story, so this change also made sense. BTW, I liked Sean Bean as Odysseus, and would like to have some more of his character, maybe even the scene of his own unwilling recruitment. Sequel, anyone? 
Sacking of Apollo’s temple: I don’t recall any similar scene in any of the literary traditions. I think this is a reference to the Greek sacking of the nearby town of Thebe, from which Agamemnon abducted Chryseis, the daughter of the priest of Apollo. The movie seems to conflate the sacking of Thebe with the sacking of Lyrnessus (another nearby town–the Greeks got bored sitting outside Troy), which had occured much earlier in the Trojan War. It was in the earlier sacking of Lyrnessus that Achilles abducted Briseis–however, I don’t believe she was ever depicted as a priestess of Apollo, and I’m not sure if she was Paris’s cousin (though with 49 brothers, it wouldn’t be surprising of Paris was related to everybody in Asia Minor in some way or the other). Furthermore, in the literary accounts Apollo does punish the Greeks for desecrating his temple, by sending plague onto their troops, whereas in the movie Achilles rather brazenly scoffs at the idea of Apollo seeking vengeance.
The feud over Briseis: in the movie, Agamemnon immediately takes Briseis away from Achilles once he’s learned that she was among the “spoils.” In the literature, this only occurs much later that the sack of Lyrnessus–after Chryseis’s father pleads with Ag to give her back to him, he does so, but only after he’s forced Achilles to give up Briseis to compensate him (and to punish Achilles for having a smart mouth). The movie simplifies these stories by streamlining the characters.
The warriors: the Iliad of course is full of them, and tells you who each guy’s father is–even guys who only show up to get beaned by Achilles. I was a little surprised at the omission of Diomedes on the Greek side, however, and it would have been nice to see Sarpedon on the Trojan side. As for Ajax (the Great–Ajax the Lesser isn’t in the movie), he dies too soon–in the literature, he doesn’t die until after Achilles’ death, and so not at Hector’s hand (Ajax actually commits suicide).
Paris vs. Menelaus: actually follows the literary tradition pretty well, up until the end of the scene. Paris really is pitiful. In Homer, he’s escorted away (by Apollo? or Aphrodite), and then Menelaus claims victory. The movie’s twist–by having Hector defend his brother and actually slay Menelaus–works well dramatically, but it’s in total violation of the literary tradition. After all, Menelaus should survive the Trojan War, and return to Sparta reconciled with Helen.
The Trojans fighting the Greeks at the ships: for the most part, this scene is nice, and follows the Iliad’s depiction of the Trojan resurgence (during this time, Zeus orders the other gods not to interfere with the battle, and without Athena’s assistance, and with Achilles still sulking in his tent, the Greeks don’t far very well). However…the Trojan attack with balls of twine rolled over flames to make Great Balls of Fire is just Hollywood cheese.
The death of Patroclus: here, the movie takes considerable liberties while still maintaining the essence of the story (i.e., the one thing that gets Achilles off his ass is Patroclus’s death). In the movie, Patroclus is a kid–he’s never even seen battle. In Homer, he’s a formidable warrior, though young. In both versions, Pat borrows Achilles’ armor, and the Trojans at first think he’s Achilles. However, in the Homeric version, Hector recognizes it’s Pat before he fights him. When he slays Pat, Hector is actually pretty happy, and fights over Achilles’ armor (which he strips off the body)–unlike the movie, where Hector doesn’t even realize it’s Pat until after he’s dead, and senses his doom when he learns it’s Achilles’ cousin.
Hector vs. Achilles: the movie also changes things quite a bit with this scene, but I have to admit that, with all due respect to Homer, I actually prefer the movie’s depiction. In the Iliad, we see Hector turn tail and run away from Achilles. And run. And run. In fact, he runs around the walls 3 times before he finally stops and turns to face Achilles (and that’s only because Athena has appeared, disguised as Hector’s brother Deiphobus, and tricked him into thinking he’s got some reinforcements). It has always bothered me, because Hector has seemed like such a valiant warrior up until this scene and it just doesn’t seem in character for him to run away like that–even when facing the mighty Achilles. So I thought the movie’s show-down was more effective. One line, however, is almost a direct quotation from the Iliad: when Achilles tells Hector, “There can be no pacts between lions and men!” A nice touch.
Achilles and Priam: this scene, plus Achilles dragging Hector’s body around, pretty much follow the Iliad. Only difference is that a few more days transpired between Hector’s death and Priam’s visit–during this time, Achilles held the funeral games for Patroclus, and every morning he drove his chariot around Pat’s pyre, dragging poor Hector’s corpse behind.
The Trojan Horse and the sack of Troy: the movie really sped things up to get to this scene. By this moment, both armies should be pretty much depleted and exhausted (10 years of siege!). Plus, Achilles should already been dead, slain by Paris. Paris should also be dead by this moment. Briseis? I guess she’s still with Agamemnon–Ag never gave her back to Achilles, and I think the last appearance she makes is at Patroclus’s funeral. The movie also leaves out the skeptical Trojans–like Cassandra and the priest Laocoon–who warn their fellow citizens against taking the horse into the city. The sack of Troy follows the spirit of the literary tradition, although it changes things by including all those characters who should already be dead. Furthermore, Andromache (like the other Trojan women) does not escape down a secret passageway–she’s enslaved by Neoptolemus, Achilles’ son, while Astyanax is hurled from the city walls to ensure that he never grows up to seek revenge against the Greeks (in fact, the fate of which Hector warns Andromache while he’s showing her the passageway is exactly what transpires). As for Aeneas, he should be a seasoned warrior, not a kid–Paris surely knew who he was (though Aeneas has* been out there in the battlefield, while Paris has been staying indoors with Helen most of these ten years, so maybe his face wouldn’t be too familiar).
The death of Agamemnon at Briseis’s hands, of course, completely violates the literary tradition, just like Menelaus’s death does, and ruins the idea of an Orestes/Electra sequel. The two brothers would survive the war; Ag goes home to meet his death (it would have been great if they’d shown him on the boatride back to Mycaenae, saying how nice it would be to get home and relax in a hot bath) while Menelaus sails home with Helen to live “happily” ever after.
But the real ending is a terrible ending, since by the end of the story your sympathies are with the Trojans more than the Greeks–at least, mine always have been. So I don’t really mind the idea of Helen staying with Paris, and all of them along with Andromache escaping from burning Troy. If only Hector could have survived, too–but his death is essential for the tragic mood of both the Iliad and the movie, so I guess I can’t complain.