During the centuries, there have been many prophets, who foresaw the end of time. From all those prophesies the most accurate and nice (with the archaic meaning of precise) were the ones of the witch Agnes Nutter. The irony is that her book never became popular. So, no-one suspected that the end was very near.
Or the ones that were aware of the end of the world were only a few entities and perhaps a human. The descendant of Agnes Nutter, Anathema Device, had in her possession the only copy of Agnes' book. Also, Crowley and Aziraphale, a demon and an angel, knew very well that this was to be expected as a part of a bigger plan. Indeed, Crowley was the one that changed a human baby with the baby Antichrist. But, a little problem occurred: both Crowley and Aziraphale came to like the Earth and the people on it. As a result, they didn't want for it to end and to go into a war between Heaven and Hell.
This is one of the most interesting stories I've read about the end of the world. To have an angel and a demon be friends for many centuries and unite in order to save Earth was a brilliant idea. I liked the fact that every little action did matter for the outcome of the story. Even when a new character was introduced very close to the end, it was immediately obvious that he would make a difference. Eventually, the story was as crazy as I'd expected it to be.
The characters were a little problematic for me. Crowley and Aziraphale, as well as Anathema Device and Adam Young, were all very likeable and well-developed. But, there were also numerous other characters that appeared in a very small part of the story and thus I couldn't relate or care about them. Those, in fact, were the parts that I had difficulty to get through.
What I really liked about Good Omens is the idea that nothing is purely evil or purely good. This is the human nature and every single character in this novel proves that. Most of the great triumphs and tragedies of history are caused, not by people being fundamentally good ot fundamentally bad, but by people being fundamentally people.