My classics lecturer mentioned that this play was rather ho-hum and in a way I am inclined to agree. However, we still need to consider that it is an Aeschylus play, which means that it was at least a generation earlier than the plays of Sophocles and Euripides. Aeschylus is considered to be one of the great dramatists of Classical Greece, however since we only have plays from two other tragedians that doesn't really say much.
Aeschylus' plays do tend to be more primitive than those of Sophocles and Euripides and generally focus more on the myth rather than making any particular comment on society. However, each of the three playwrights (and I do not include Aristophanes in this group as he wrote comedy, not tragedy) have their own styles and purposes. I like to compare them with modern directors and would suggest that Aeschylus would be close to a Frank Capra, Sophocles would be a Ron Howard (or a Stephen Spielberg) while Euripides would be a Martin Scorsesee (or a Quentin Tarantino). I've probably said that before, but I like the comparison (though I would love to hear from you if you disagree).
This play is about the Daenids, who happen to be the daughters of Daenus (which is probably pretty obvious). The story goes that after Io was transformed into a bull by Hera (simply because Zeus slept with her – isn't it interesting that the victim, not the perpetrator, is the one punished) and was tormented by a gadfly, forcing her to flee to Egypt. She settled down in the land of the black earth (which is what the Egyptians called Egypt) and from her descendants came the brothers Daenus and Aegyptus. Daenus had fifty daughters, and Aegyptus had fifty sons, and the sons wanted to marry the daughters. However, the daughters did not want a bar of them, so they fled with their father to Argos for sanctuary, and the entire play is about the conflict between the sons of Aegyptus and the daughters of Daenus. In a way it is not all that thrilling. However it is not Aeschylus that we criticise, but rather the people that decided to include this as one of the plays that would survive.
So, first I will talk a bit about Argos. Having read through some of these plays I have noticed that the Mycenean Greeks (the period in which the plays are set) refer to the Greeks as Argives or Achaeans. Now, Argos (the land from which the Argives come) lies on the northeastern corner of the Peloponese and Achaea lies on the northwest. As such it is only a part of the whole Greek world. But, during the Mycenean period, Argos was the centre of Greek life. While there were other city states (such as Athens and Thebes) the powerbase during this period lay in Mycenae, which is located in Argos. This is probably why we see the Argives being referred to as Greeks (though Greek is actually a Latin term, the Greeks refer to themselves as Hellenes).
Then there is the idea about Egypt. Remember, the world revolved around the Greeks and as such it was the Greek race that gave birth of humanity. Here it is suggested that the Egyptians originally came from Io, a Greek, however we know a lot differently now. Consider the date of the play: 500 BC. By this time Egypt was a province of the Persian Empire, having collapsed as an independent entity after being invaded by Babylon (and Assyria before that). Yet, if we move earlier to Mycenaen Greece, we set the time at around 1500 BC to 1100 BC. Once again we are in the New Kingdom of Egypt, and archaeology proves that Egypt had been around for a lot longer (in fact much longer than the Greeks). Well, the Greeks weren't scientists though, nor did they have sophisticated archaeological techniques (they had only just developed the discipline of writing history), but in the end it is all irrelevant because this is mythology, and mythology is generally skewed to support a point that the mythmaker is trying to make (we see it all the time in our society – it is called propaganda).