I never seen Alexander, but from what I heard the film is terrible. I seen 300 and two cuts of Troy, the theatrical and director's cut. 300 and Troy are two different kinds of film, with 300 being a popcorn movie where you can watch without any thought, while Troy is the drawn out epic.
The director's cut of Troy is over three hours long. I think the added content does improve the film but it could just be made because the theatrical cut was considered a failure. One thing I liked in Troy was the city itself and the Trojans. I think one problem is that when people think of the Trojan War, they probably assume that Troy was the villains, and I think if it was trying to be a simpler film it might have done that, but instead the Trojans are portrayed as simply trying to defend their homeland, with Hector ending up being probably the most heroic character in the film. I also like how some of the Greeks, like Odysseus, may not agree with the war or Agamemnon, but the come along anyway as an act of duty to their lord. One thing I didn't like was the armours the people wore. They didn't seem distinctive enough, but I don't know anything about bronze age Greece.
I think one problem with the film that some people had was some of the casting choices. Having Brad Pitt as Achilles people will watch it and think it's just Brad Pitt and not Achilles, although the way he played the role does suggest a character that is only there just for his own glory, which in a way I guess makes sense to have a big name actor since that would probably be the closest equivalent to a renowned hero that everyone knows. Another problem is Orlando Bloom, who seems to act the same in every film, even in more grown up roles.
I never read any of the epics that the film takes it's inspiration from, so I don't know how it compares to them. I know the director said that Iliad may have been what started the idea for the film, many of the elements were taken from Virgil.