With the Heliconian muses let us start
The genitals, cut off with adamant
And thrown from land into the stormy sea,
Were carried for a long time on the waves.
White foam surrounded the foamy flesh,
And in it grew a girl.
The married man
Who gets a good wife, suited to his taste,
Gets good and evil mixed, but he who gets
One of the deadly sort, lives all his life
With never-ending pain inside his heart
And on his mind; the wound cannot be healed.
The greatest thing about Hesiod's Theogony is that it's short.
It was of great importance to the ancient world for other reasons as well, but this does not translate into a particularly rich experience for the modern reader. Unless he or she is an historian or a classicist interested in the Greek worldview.
"Theogony" means origins of the gods and Theogony is mainly about how the Olympian gods came about. After a long imploring of the muses, it starts with the forming of the world from Chaos, which at the time meant the gap separating Heaven and Earth.
Apparently it happened like this: "Chaos was first of all, but next appeared / Broad-bosomed Earth...." Just like that. Pretty dramatic, huh? And we thought the old Greeks were such deep thinkers. It carries on with various entities lying with each other and giving birth to various other entities. Except for Dark Night, who sleeps with no one but still gives birth to Distress and Blame. It's a strange world. Almost as bizarre as that of Genesis in the Old Testament (which was being worked up about the same time, just around the corner of the Mediterranean).
You may notice a logical problem in the passage quoted above. If Chaos was what separated Heaven and Earth, then how could it then give birth to Earth? This kind of contradiction gives scholars the idea that Hesiod did not originate the creation story himself but patched together several previously existing, not-quite-compatible accounts.
As the story progresses, the gods come into various conflicts with each other, revolutions take place and the gods we know from other Greek myths, headed by Zeus, come to power. Some of the gods also start fooling around with mortals and we learn the origins and background of famous earthbound figures of mythology, like Jason, Calypso and Odysseus.
You'd think in all this there would be some bloody good stories of intrigue, backstabbing and titanic battles. There are many such bloody stories, but they're told so badly that the reader never becomes involved.
So, maybe Hesiod wasn't trying to tell good stories but just to lay down the basics of what the Greeks should believe about the world. So read this Hesiod if you're interested in that kind of thing. Otherwise stick to Homer.
My copy of this is the Penguin volume translated by Dorothea Wender and also includes Works and Days, as well as work by Theognis. I couldn't say if any other translations improve Hesiod's work.