If this movie had wrapped things up about 5 minutes after the 'sudden snowstorm on the highway' I'd be raving about how great this movie is. Up to and including that point there are a lot of twists, neat visuals, tension, etc.

Unfortunately it stumbles on for a long while after that scene, with the characters' actions becoming increasingly braindead. At the end it's so bad that a character desperately needs to bust open a window, and has lots of rocks available to him, but it keeps beating on the window with his hands.

It's worth renting/borrowing to see the strong first part. The less you know about the movie, the more powerful the first part will be.