Our narrator isn't an eyewitness to the events of the story—he's just some shlubby guy who likes to write poetry. Instead, he asks the Muse (the goddess of poetry) to inspire him with knowledge of what happened long before his time.
What the Muse tells him (i.e., what we see when we read the Iliad) is mostly the actions and words of men and women. We do get some limited insight into characters' minds—especially when they are deciding between several courses of action—but most of the time we learn about their thoughts from what they say, like in a play.
Within this framework, Homer's narration is extremely even-handed. Not only do we learn about what is going on among both the Achaians and the Trojans (though the focus is a bit more on the Achaians), we also get to see the conversations and actions of the gods—the whole pantheon of 'em.
This last feature (plus the poet's apparent knowledge of the ways of fate) must have struck his original audience as pretty amazing. At least we hope it did... because it strikes us as totally incredible.