Sometimes trailers are completely misleading about a film, but other times they're right on the mark. The trailers for
Identity happen to be a bit of both. There's no chance you can guess from the trailer how
Identity will be resolved, but if you got the impression that film will be a muddled mess of different ideas and themes, you've got the right idea.

Up until the final third of this film, I was impressed.
Identity seemed to be a very solid thriller, creating a suspenseful mood most films don't touch these days.
And then the film fell apart. I bite my tongue to avoid spoiling it, in case I'm alone in my distaste for the twist, but the film totally changes. It doesn't simply go through a plot twist... It takes a wholly different direction, at which point I felt like I was watching a deranged episode of
Inside Herman's Head. By the end, it pulls itself together long enough to leave a minor impact on your cranium, but I wouldn't doubt if you're left wondering, "What happened to the good film I'd been watching? I want the rest of it!"

That said, you won't be bored to tears.
Identity has some captivating cinematography, bathing the characters in darkness and drabness, very reminiscent of classic film noir. That, in combination with some responsible, suspenseful pacing, will keep chests pounding and butts on the edges of seats.
Final
Don't waste your time or money seeing
Identity in theatres. When it comes to DVD, rent it. Don't bother paying full price to buy a ticket or video... You'd be getting ripped off, as you'd only be getting two thirds of a good film.