Personally I thought that the odd looking fantasy-armor was an interesting way to highlight that what we are seeing is a story, not history. As highlighted by the storyteller in Odysseus' palace. But I think it also ties in thematically with the heroes-and-monsters aspect.

The first we see of Agamemnon is his crazy armor with the golden spine running down the back of the helmet, and it immediately establishes that some people in this story are much larger than life, so much so that they seem sort of monstrous and offputting. Agamemnon looks like Darth Vader, striding forward in that black and gold armor. And in a way, Agamemnon has made himself a monster to achieve his personal ambition, sacrificing his daughter at the outset. When he's later killed in bed by his embittered wife, it's in maybe the one scene of the movie where we see him without his armor - having returned home and stripped it off. Perhaps he thinks he can be a person again. But he is no longer the man he was, and his home too has become hostile to him. In making himself a legend, he has shut himself out from the life he had.

More broadly, he (and the kings who went with him) has perhaps even destroyed that way of life entirely by violating larger social contracts, such as taking Troy by a deceptive offering to a shared god. Which is the core shame that's hounding Odysseus through his trials (along with some survivor's guilt).

Anyway, I was pleasantly surprised by the movie. It felt both familiar and fresh at the same time, and made a lot of initially odd seeming choices that I wound up finding interesting and thematic.

Big recommendation.