Workable premise marred by clumsy writing

So here we have what should have been a terrific movie or at least a seriously fun guilty-pleasure kind of deal, what with the likes of the gorgeous Halle Berry, the always-glamorous Bruce Willis and a majorly creepy Giovanni Ribisi, all excellent actors. The film is decent for the first half hour but then, thanks to sinfully poorly written scenes, it deteriorates into a banal mish-mosh. The Big Surprise at the end is the clumsiest part, which is a shame because it could have worked - there were enough 'clues' (along with some disturbing dream/flashback sequences) thrown in to warrant this ending but it just falls flat. In all movies, and particularly in this kind of a movie, execution is everything (no pun intended).