Gnostic Texts - Is Apocryphon of John the Way to Go?

If you want to read a really fantastic Gnostic text, then Apocryphon of John is the way to go. It basically retells what people thought they knew about the universe. But that's where I sort of join with those that worry about calling Gospel of Thomas Gnostic in those senses. And so it seems like if you would define the term anyway, do you have a 30-second description of Gnosticism?