It took a bit explaining and re-explaining to Paul. But basically, there are angels, there are demons, and it's not quite so easy to figure out the difference between the two. But what's more important is that the Son of Satan has been mis-swapped into the wrong family and things don't go according to that plan either. So when the end of days comes, everyone is caught off guard.
Oh, and of course, it's all been predicted by Agnes Nutter.
The first time I read Good Omens, it was for a book club (my suggestion). And while I did laugh and thought the writing was clever, I was a little disappointed that it wasn't what I expected from either Terry Pratchett or Neil Gaiman. I did not give it a high review.
Second time around, I appreciated it much more as something special of its own - something silly and at times heartwarming - a good read.