I have to say, I didn't expect much from this. I was pleasantly surprised by how enjoyable Source Code is.

Jake Gyllenhaal gives a good performance as the sympathetic lead who's trying to make sense of the chaos he's been thrust into. What effects will his actions have? What counts as doing the right thing? What's even real?

The people running the program keep telling him to do whatever it takes; Colter Stevens is basically given a free license to do any heinous stuff he wants.

Just because everyone else is saying it doesn't matter, does that make them right?

There are some strange moral and theoretical questions (which are fun to bat around with friends) that arise from the movie's ending. The sciency stuff is interesting, but if the movie focused too much on it, it would become a bunch of jargon-laden nonsense. No, the sci-fi element is a vehicle for a story that's more engaging than the trailers or summary blurbs ever suggest. Source Code is about second (and third, and fourth, and fifth...) chances.