I thought Hogfather was really good, but not great, which it could have been. The rest of my family found it pretty bad.

The Colour of Magic was decent as mindless entertainment, but it managed to be even more random, flaky and generic than the source material, and riddled with Deus Ex Machina to boot. Haven't yet seen Going Postal, but the only reaction to it I've heard so far wasn't encouraging.

So with that track record, and the fact that Good Omens is much dearer to my heart than any of the above, you'll excuse me for harboring misgivings.