It's no more absurd than any other religious belief system. I think it's neat.
You've got the original supreme God, and beneath him, a pantheon of his god-children, called Aeons, arranged in male and female pairs. God and the Aeons exist in a kind of perfect spiritual realm. But one Aeon attempts to reproduce asexually, without an opposite-sex partner, and in so doing creates a deformed being called the Demiurge.
The Demiurge is twisted, imperfect, discontented, corrupt. Sensing its nature, its divine mother casts it out of the Aeon realm. In isolation it decides to create its own realm: our material universe. This material universe is as imperfect as the Demiurge itself, and the Demiurge convinces its inhabitants (us) that it is the supreme God.
What is the answer then? First to recognize the Demiurge's deception, and then to seek the true God. In Gnosticism, the true God (unlike the false one that proclaims itself to us and demands worship) is hidden, mysterious, withdrawn. You have to look for it; it won't present itself to you through organized religion. Christian Gnostics identified the Demiurge with the OT God and the true God with the more cryptic Christ. They believed you had to seek enlightenment through a deep inner knowing, innate, intuitive -- gnosis.
It's pretty easy to see why the ancient Christians were not fans of Gnosticism. They thought Gnostics missed the entire message about sin and forgiveness, about Christ's sacrifice for humanity. And they did. They didn't see the world in terms of sin and forgiveness, but of illusion and satori. It was like their religion was a conspiracy theory about Christianity. As conspiracy theories go, though, I think it's pretty cool.