I think how Seth McFarlane described this movie in the show The Roast of..., pretty much describes it. "There's no sense of reality. It's impossible to follow what's happening and midway through we realize you were unconscious the entire time."
Ok, no reason to get al lyrical about it. The actors were too young to be believable for my taste. All I saw were just kids (early twenty), but the concept of what they were doing was quite heavy stuff. Being this young, without much experience, pulling it off like they did... Meh. As for some scenes... You know... Those deadline-kinda scenes when seconds tick away and things to be done need minutes? Well, it doesn't help to stress that concept of getting imposible things done in time by showing these scenes so many times that the three seconds left actually start to feel like three hours and you start hoping the whole damn does blow up.
But now on the more positive side. I love the concept of the mind games. Also the main character actually had a deeper layer to him. The loss of his wife in the way that he did, I really liked it. I just love seeing people suffering on the inside. Regrets, loss, pain and letting go. Nice one. They also did a great job not explaining too much. But in the end. I just refer back to Seth's quote.