For starters, the Odyssey has a clearly defined protagonist (i wouldn’t really consider Achilles the protagonist in the Iliad. He may be a central character, but not as involved in the main story as, say, Agamemnon, and there are so many different plot threads there really isn’t only one protagonist)
Secondly, the Iliad has a single location and is all thematically linked by the siege of troy. On the other hand, the events in the Odyssey are much more varied and, while they are all related to Odysseus’ return home, they are largely interchangeable. The Iliad, on the other hand is much more cohesive and structured, because it’s basically following a war journal, and wars generally have a fairly rigid progression. Sieges especially.
You can’t put Hector’s death after Ajax’s suicide, and you can’t put Cassandra’s rape before the Trojan horse. However, you can easily switch around Polyphemus and Schylla and Charybdis and, geography aside, you would not lose anything because the events in the Odyssey are self-contained. For the most part, anyway.
Also, most of the people who show lack of morality or humanity, on either side, are made examples of, either by straight up punishment or divine retribution, poetic justice or by demonization by the narration itself. Odysseus, especially, for his trickery is punished with an entire epic worth of divine retribution, even though he was on the “good side”. Also, Ajax’s (one of the few actually honorable fighters in Agamemnon’s service) suicide is pretty much on Odysseus’ head as well.
Which brings me to another point: Either there are no “good guys” or the jist of the story is “don’t side with the guy who contradicts the gods, because he will make it home safely, but you won’t!” And so far i haven’t had a satisfactory answer aside for the obvious “doesn’t matter who you’re fighting for, don’t be a dick” moral, which doesn’t really clarify the issue of who was in the right there.
Then again, the Greek were ahead of their times, and probably figured out gray moral quandries well before we did. No wonder the Eneid is so fucking boring by comparison.
So, basically, The Iliad did what Game of Thrones does before Christ was even born. How about them apples.