The trailer for What Lies Beneath is far more revealing than I'd like, but upon seeing the film it doesn't give away as much as we're inclined to believe. There are some good surprises left in the film. Still, if you don't like the actors it's probably not a good bet for you.
I enjoyed the film but not quite as much as Jack, I'd give it a B+ rental and a B/B- theater rating. I felt there was too much reliance on gimmicky tension building devices ---- can we dispense with the "standing-with-the-fridge-door-open-rooting-around-while-the-music-builds-to-slam-the-door-and-SUPRISE-there's-somebody-standing-there" scene? This has been done and done and done. It just makes me fidgety and pisses me off. Ditto the backwards walking thing. At least they didn't have a cat jump on anyone off a tall bookcase. Couldn't quite bring themselves to forego the "repeated-endangerment-caused-by-illogical-and-totally-brainless-actions-on-the-part-of-the-fleeing-protagonist" schtick, though so I had to mark down for that. I know some people like these devices so you can take all of this with a grain of salt if you're less bothered by them than I am.
On a more general note I felt that the film could have been stronger if they'd really let the audience believe that maybe Pfeiffer was losing her mind rather than communing with ghosts. There was plenty of room in the script for this and I got the impression that they might've intended to play up this angle a bit more and then changed their minds because of the success of recent horror/suspense films.
All in all it's a decent little film with some good twists and nice performances and a couple of really great scares achieved without "cheating". You won't feel ripped off if you pay full price.