Agamemnon is part one of Aeschylus' "Orestia", a trilogy of plays. I knew the story of Clytemnestra murdering her husband Agamemnon, King of Argos, for his sacrifice of their daughter, Iphigenia, and I knew that a cycle of revenge followed. What surprised me was that this vicious cycle didn't begin with Agamemnon's sacrifice, but with Agamemnon's father, Atreus. Atreus had boiled his brother's children, fed them to him, and thus brought a curse upon his family.
The play has a very ominous feel and is full of foreshadowing of the events that will soon take place. Cassandra's bloody prophecies were especially chilling.
I have never liked Agamemnon in any book or movie I have seen him in and this play was no exception. The descriptions of Iphigenia's pleading especially turned my sympathies against him. I can't say I felt bad for him. Clytemnestra seemed like a more sympathetic character at first, but at the end I think it was clear that revenge had consumed her. The character I sympathized with the most was Cassandra. The way her grim prophecies fell on deaf ears reminded me of Lucy from Sweeney Todd, trying to draw attention to the foul deeds on Fleet Street (the implied cannibalism and revenge plot also reminded me of Sweeney Todd - I wonder if there was an influence there). It was also really unfair of Clytemnestra to murder Cassandra along with Agamemnon. Cassandra was Agamemnon's mistress, fine, but it was hardly her idea to become his slave.
As might be expected, the play ends with promises of future carnage.