'Reign Over Me' is listed as a comedy. Throughout the first half of the movie, that holds true. I can tell you that by the end of the movie I was no longer laughing. Adam Sandler has definitely found his golden apple.
Semi-Spoiler:
It isn't often I'll make mention of something as trivial as a movie. I can tell you that in the end of the movie he thinks about doing something that would make most people squirm, but you generally feel for the guy by the end of it and understand what it is he is going through.