Peter Ericson’s review published on Letterboxd :
This is one of those movies in which the viewer finds out, piece by piece, what is really going on at the same time as the protagonist does. This is also one of those movies that grow on the viewer upon post-movie reflection. Depending on the intellectual effort one is willing to engage in while watching the film, "Source Code" is either a solid, suspenseful thriller with elements of science fiction or a solid, suspenseful thriller with elements of science fiction plus a thought-provoking philosophical meditation on the nature of reality.
Clocking in at 93 brisk minutes, "Source Code" is a refreshingly short movie. Ben Ripley’s tight and effective script wastes no time as it tells an intriguing story. Duncan Jones handles the material in an admirably economical way, and his resourcefulness as a director allows him to make the most of every second of the film’s running time.
Initially, it may seem like character development will be scant, but as the movie unspools, one starts to care about the two central characters, Colter Stevens (Jake Gyllenhaal) and Christina Warren (Michelle Monaghan). While their fate is perhaps not as thrilling or unexpected as much of the rest of the movie, the filmmakers succeed in making it less cloying than it could have been, and the characters have arguably earned the kind of closure suggested by their final scene together.
What happens in the Source Code universe can obviously differ to some degree from what happened in reality before the bomb exploded. Considering what the viewer is told at first about how the technology behind the project works, that fact may appear to be a plot hole, but it’s actually perfectly logical, at least in the context of the film. The fairly elegant explanation comes at the end of the proceedings. That revelation also puts the events of the movie in a whole new light, thereby ensuring that "Source Code" ends on a surprising, sobering note.
Don Burgess’s crisp, somewhat cold cinematography—the opening sequence features striking aerial footage of Chicago—gives the picture a sense of immediacy that goes hand in hand with the fast pace of the film. The score, composed by Chris Bacon, helps to build atmosphere and subtly hints at something with profound implications going on beneath the surface.
Gyllenhaal ably carries "Source Code" on his shoulders with a strong performance. He and Monaghan, who winningly plays Christina, have good chemistry together, which makes their relationship come across as genuine rather than as a script contrivance. In the role of Colleen Goodwin, Vera Farmiga has little to do for most of the movie, but a few meatier scenes in the last act afford her an opportunity to make an emotional impact on the viewer.