I know nothing of the Iliad so can not comment on it's accuracy to that story. However, as a stand alone film I found this very boring. The battle scenes tried to be large and spectacular but they were just obvious CGI.
The acting is poor and no doubt Brad Pitt was cast just to attract the ladies. But he does not make a good warrior, too pretty i am afraid.
Good points are is the design. This film does look good with the landscape and castle buildings/walls impressive. I do like a film that at least tries to get the characters accents true but this film just seems to ignore it completely. we hear American, Scottish English anything but what you might expect for a film about an ancient eastern civilisation.
All in all, I do not recommend this film for a family sit down. It is too long and the young will get bored.
For adults, it is OK if you don't care about the lack realism.