An underdog story, an uplifting tale, coming of age, rebellion, teenage love, dreams in miracles and impossibilities, archtypal overbearing naysayers and doubters, last minute self-doubt when the chips are down only to have everything come together perfectly. All the elements are here. I've read some of the critical reviews of the film and I think I agree with the two that are quoted in the Wikipedia entry for the movie.
Stephen Holden (NY Times) said, "This crude, inspirational tear-jerker is as sweet as a bowl of instant oatmeal smothered in molasses."
Sean Axmaker of the Seattle Post-Intelligencer thought the "conventionally heartwarming underdog drama doesn't miss a cliche."
I could warn you about spoilers, but if you can't predict the vast majority of the script, then you haven't seen many movies.
It has inspirational moments, and it has been pointed out that Campbell Scott in his role as the priest with doubts his faith (but believes in Ralph) does shine in his role, one of the few I found believable. I enjoyed the use of "Hallelujah" by Leonard Cohen and performed by Gord Downie at the beginning of the film's climax. Jennifer Tilly as a Canadian nurse? Didn't work for me. I could imagine that for someone who is a strong Catholic, the imagery and Saintly references may have made it a more compelling film.
In sum, I don't want to be too hard on the film because I am looking for good films about running and this is more of a coming of age film that happens to incorporate running. In that genre, it did reasonably well. I have not watched many fictional films about running and I am not sure how many I have in my queue (I do need to go back and watch "Run, Fat Boy, Run" again) but I doubt this is one I'll feel the need to watch again.