If libations were proper to pour above the slain,
this man deserved, more than deserved, such sacrament.
He filled our cup with evil things unspeakable
and now himself come home has drunk it to the dregs.

This is a morally complex play for a modern reader. At first we side with Clytaemnestra, who claims to have remained faithful to her husband, while he has been sleeping with concubines and has killed his daughter. We cheer when he is killed by Clytaemnestra. But then we learn that she has had a lover all along, and the chorus almost unfailingly takes the side of Agamemnon. I don't know what I'm supposed to think. I don't know for sure what the Greek audience would have thought. I look forward to discussing this play in class and maybe understanding it better thereafter. I do think these lines, from near the beginning of the play, are relevant to the question:

A man thought
the gods deigned not to punish mortals
who trampled down the delicacy of things
inviolable. That man was wicked.

Also something WEIRD is going on with gender roles in this play. Merits thinking about.