It was based on the Illiad insofar as it used the same characters and the same situation: Helen is "kidnapped" in an affair and Greece wages war on Troy.
However, the timeframe is much shorter. Rather than a war that takes a decade to fight, it takes about 12 days. Achilles, rather than being some souped-up superhero like in the mythology, is much more a feeling, thinking human being who has some wordy scenes in which he reflects on the nature of his role in the life. These two points are what mythology fanboys cry about. I for one, didn't mind that much. An introspective Achilles was nice, and the war made just as much sense in 12 days as it would have in ten years.
Yes, Legolas (sorry, I won't call him by his real name because he sucks too much, like the time I went and saw all the blooming flowers in Orlando) was a total coward. Like his character in LotR, he's an archer, but this time a really wussy one who has no reason for swooning such a hotty like Helen. He must have a big **** or something. Anyway, in mythology he did kill Achilles, but the way it was handled in the movie was far too lame and cowardly.
Plus, the first shot into Achilles' heel (yeah, where we get the phrase from) was not some doom shot that changed everything, it was just the first in many shots by a cowardly little wuss who didn't listen to his own pleading cousin to stop making Brad Pitt look like a porcupine.
The movie was a blast to watch. Achilles and his Myrmodins (sp?) were awesome, and the character dialogue was nice. Legolas was the only part of the movie I actually hated. Sadly, Legolas and his wussy archery skills *were* the ending of the movie. Bleh.
