Source Code movie a source of confusion?

Starring: Michelle Monaghan, Jake Gyllenhall

Category: Science Fiction, Thriller
Source Code is hard to pin down and harder to categorize. While it clearly makes itself out as an action-suspense thriller, the main thrust of the movie is science fiction. The idea behind the movie is that the military has found a way to go relive another person's life for 8 minutes in the past. They could send someone, in this case pilot Colter Stevens (Jake Gyllenhaal), to re-live the last 8 minutes of someone else's life who has died. Stevens is re-living the life of Shawn Fentress, victim of a train bombing. He is riding the train with Christina Warren (Michelle Monaghan) on the way to work.

At first Stevens is disorientated but with the guidance of Captain Colleen Goodwin (Vera Farminga) he begins to learn the limitations and capabilities of his capability. Goodwin and Dr Rutledge, the man who build the machine, want Stevens to focus on finding the bomber, who they believe is on the train. But Stevens wants to find and disable the bomb. Goodwin and Rutledge try to convince Stevens that the reality he is in is a simulated world and that the events have taken place. So disabling the bomb is useless. At the end of each 8 minutes, Stevens is pulled out of the world and back into the machine. Each time he is sent back, it begins at the same place and the same things happen again. But Stevens begin noticing that although each 8 minutes he re-lives is basically the same, some small differences do happen, which gives him hope that he can change things.
Meanwhile, he begins to learn of his fate and how he came to 'pilot' the machine. He learns about the lost time in between his last memory of Afghanistan and where he is now. He also begins to connect with Christina and falls in love with her, much to the chagrin of Goodwin. But it is this connection that keeps him going as he falls into a state of despair as each attempt fails to reveal the bomber.
The movie is quite successful in being suspenseful despite working within cycles of 8 minutes and recurring events. Stevens goes through a process of elimination as he investigates each suspicious passenger. He evens 'builds' a plan to get a gun in an attempt to go after a suspect, making progress after each 8 minutes.
Halfway through the movie though, I struggle to push out the spoiler thoughts while I tried to enjoy the movie as it is. For those that can tune out, this is a great 'ride' movie. But to even a casual science fiction fan (if there is such a person), its very clear where the movie is heading even though they don't know how it will end. 
The characters were believable in their own way. Stevens is the driven hero but is made human with his regrets. Goodwin is sympathetic to Stevens' situation although as being in the military, she will follow orders when given. And even though her character is somewhat limited and repetitive (being the only main character that exist only in the 8 minute cycle) Michelle Monaghan, is able to make the most of it and able to portray Christina as a woman clearly at the crossroads in her life when it comes to love and life. The one most identifiable to me is Dr Rutledge, the myopic scientist in pursuit of his goals (some of them not necessarily scientific in nature) and discarding other conclusions than his own.