Both these descriptions ("clear and poetic") of the Iliad's style might seem kind of a contradiction. For many readers, the language of the Iliad seems weird or formal—or, at any rate, far from clear.
And yet, you have to look at Homeric language as more like a foreign language, or learning a new dialect. Once you get the hang of his usual way of saying things, you'll realize that he's almost never being complicated for its own sake. Actually, he's almost never being complicated. He just says things in a very clear and direct way... but in his own distinctive language.
As for calling it poetic, this might just seem redundant: it is a poem after all. But because of that, it's important to be aware of the distinctive features of Homer's poetic style.
Probably the most famous of these is the so-called "Homeric simile." The first of these similes comes in Book 2:
They swarmed like bees that sally from some hollow
cave and flit in countless throng among the spring flowers, bunched in
knots and clusters; even so did the mighty multitude pour from ships and
tents to the assembly, and range themselves upon the wide-watered shore,
while among them ran Wildfire Rumour, messenger of Jove, urging them ever
to the fore. (2.87-92)
These lines have the three ingredients of any Homeric simile: (1) saying what the thing you're talking about is like (in this case, the army is like bees); (2) describing the thing you're comparing it to (bees); and (3) reminding the audience of what you were originally talking about (the army). The third step is necessary because sometimes the description in part 2 can get extremely long.
Keep an eye out for these similes; some of them are very beautiful (and uber-famous).