Ah, it kills me to do this: An Oresteia is not that great.
What it wants to be is great. It wants to weave the three great Greek tragedians (Aeschylus, Sophocles and Euripides) into a collaboration about the House of Atreus that will allow its readers to get a feel for all three, as well as a coherent story. And by a terrific poet and translator, to boot! Sweet!
And it gets off to a promising start, too, with a terrific rendition of Agamemnon. I've read two other translations - Fagles and Hughes - and this one stands up just fine with them. Closer to Fagles: more accessible than Hughes, with the occasional terrific punch of a line that people never seem to acknowledge when they talk about Fagles.
But it goes downhill from there. Elektra just isn't Sophocles' best; it's a retelling of Aeschylus's Libation Bearers, and it's not as good. Not the fault of the translation, just the way it is.
And by the time we get to Euripides' Orestes (again, not his best work)...I kinda felt like Carson was losing interest. Euripides is a brilliant playwright - sly, nasty, modern, complicated and brash - but Carson picks up on his impish habit of upending themes and tropes and takes it as simple mischief, instead of the deadly serious commentary Euripides intended it to be. She includes modernizations that are badly out of place. (I marked one or two, but my book's not with me - will try to get them in later.)
So in the end I think Carson's Oresteia more or less fails. It's fine to read, but its goals are higher than its reach.