The Telegraph : Source Code review.

Source Code: Seven Magazine review, by Jenny McCartney

The first rule of Source Code is, don’t think too deeply about Source Code. Duncan Jones’s film belongs to the head-scrambler variety of thriller, in which scientists meddle with time and space for your viewing excitement, and its chief asset is its unflagging momentum.
Captain Coulter Stevens (Jake Gyllenhaal) – an ex army commander in Afghanistan – finds himself on a train, opposite a smiling brunette, Christina (Michelle Monaghan) whom he doesn’t recognise. She knows him, though, as a teacher who travels on her train every day of the week.
After eight minutes, a bomb on the train explodes, killing all the passengers. Coulter comes around in a dark chamber to a conversation with his handlers, who are using “time reassignment” technology to keep returning him to the train just before the explosion until he discovers the identity of the bomber: with each session, he will have precisely eight minutes to get as far as he can with his investigation. It’s Groundhog Day with dynamite.
The trick of this film is to keep the constant tick-tock of tension alive, and this it does with skill. For the viewer, there is something mesmerising about the perpetual return to the same situation, to which Stevens brings a different consciousness each time: pursuing false leads, yelling at the passengers, noticing freshly incriminating details.
Yet for all the hectic, claustrophobic weight of his character’s circumstances, Gyllenhaal retains some lightness of being, the occasional ability to crack open a radiant grin; Monaghan, too, has the movie gift of appearing at once ordinary and luminous, a girl unwitting of her fate even as disaster thickens around her. With each encounter, Stevens grows more attached to her, begging the question: how many eight-minute segments does it take a man to fall in love?
Only at the end, when the film tries to slow down, do things fall apart. There’s what looks like a perfect, poetic ending – and then the plot dully trundles on past it, layering soothing improbability on top of a working fantasy.