The Relic was not a good horror movie. I only saw it because it was set in Chicago's Museum of Natural History and I've been there enough times to have found it a nifty setting for a film. The plot was too Alien-derivative for me though, so I've never given it a second thought.
Until recently, that is, when someone recommended to me the book series by Douglas Preston and Lincoln Child that starts with The Relic. They're apparently mystery/thrillers with a supernatural bend to them and that's exactly the kind of thing I'd enjoy. Knowing how a great book like The Keep can become a crappy movie (even in the capable hands of Michael Mann), I'm inclined to give the Preston/Child series a try. (Then, while I'm thinking about it, I need to go back and read F. Paul Wilson's follow-up novels to The Keep.)