GOOD OMENS is a collaboration between Pratchett and Gaiman. According to the introductory interview with them at the start of the book, it came about because Gaiman wrote half a short story, but he didn't know how it ended. He sent it to Pratchett, who didn't know either. But he did know what happened next. So half a short story became one very very good book.
Originally published in 1990, GOOD OMENS was written as a collaborative novel in the days before high speed internet connections - in fact according to the same interview a 1200/75 baud modem (yes kiddies, we used to use them - and we had electricity and everything), was eschewed as a communication method as it proved slightly less efficient than underwater yodelling and instead a bizarre method of messages in different working times exchanged via Ansaphone's was employed. (Yes - we used machines with little tapes in them - in the house - to record phone messages.)
The problem with a Divine Plan is that there's always somebody that forgot to read the requirements specification. Nun's can get it wrong. Avenging Angels (who can be such fussbudgets) and Fast-Living Demon with a passion for posh cars don't have to look forward to the coming Rapture. When you've lived amongst Humanity for quite a while now and you're fond of the cushy gig, you may actually decide to interfere with the Plan. So as unlikely a pair as they seem, Crowley and Aziraphale are going to stop this silliness - even if they do have to kill the AntiChrist (who at this stage is really nothing much more than a naughty little boy). If they can only find him.
Obviously when you're writing high comic fantasy, the time in which the reader picks up the book becomes less problematic. But what really gives GOOD OMENS a life forever is that the central theme - the great battle of Good versus Evil - works no matter when you pick it up. Having said that, reading GOOD OMENS again in late 2007 / early 2008 and bingo - a timeframe in my human history at least - where the occasional consideration of Good and Evil, Frogs and Witches, Hogs and Devil Children - well lets just say between the hysterical laughter, just occasionally you read something that makes you go hmmmmm.
This edition of GOOD OMENS isn't the first one I've read. But it was absolutely no chore to read again. And again. And I might just pick that book up on a more regular basis for a bit of a re-read. For a collaborative novel it's hard to pick the who wrote what bits. As a novel about Good and Evil it works. As a reminder of Queen's Greatest Hits it was truly sobering. It's also dark and funny and pointed and clever and a darn good book!