If you despise the Catholic Church, you might have difficulty with this movie. If you don't want to face the topic of dying, you also might want to skip this movie.
But I'm a recovering Protestant, so I'm a lot more likely to have problems with so-called "Christian" movies done by American Christian conservatives. In fact, as a Christian, I consider it a special treat when I find a good Christian movie which is NOT your typical movie made by conservative Protestants. This is one of those rare treats, and it's the best of them all.
I also love those ennobling movies where the hero of the movie lives a life where his actions are far more praiseworthy than the life of a typical Christian -- even when the movie isn't about Christians at all. For example, Schindler's List; can you possibly have a better hero than Oskar Schindler? This movie isn't a blockbuster movie like Schindler's List. No, this is more of a "little" movie. But it might actually be as good as Schindler's List. I also liked My Name is Khan, which is far less realistic than Johnny or Schindler's List. But in that movie, a Muslim acts as heroically as any Christian ought to act. And don't actions speak louder than words?
Actions certainly speak louder than words in this movie. While the real saint of the movie is Johnny, the movie's main protagonist is Patrick. By the end of the movie, you'll love them both. A lot.