I thought it was great, but mainly because no one makes real Hitchockian thrillers anymore. If the genre were more populated there would be better flicks. The only real flaw I can come up with is that with a cast of one person, it's pretty obvious that he's not going to die, or if he does it won't be 'till just before the end credits. It took a lot of the tension out of some of the scenes- minor spoiler ahead- especially the one on the ledge outside the room.
Sam Jackson was motherfucking awesome as usual. I found myself hoping they'd pull a Psycho and kill John Cusack's character, then shift the focus to Sam, but by withholding him from us it made the scenes he was in so much more effective. Next paragraph is a spoiler, I'll put it in white text.
Having Cusack survive was majorly lame. I realize it wasn't the screenwriter's fault since it was adapted, but still. It would've been more meaningful to have him burn, then have his wife find the tape recorder in a bag of salvaged items.
I give it 8/10.