This movie is not a bad movie, but it's definitely not a comedy. I'm not saying the humor in the movie is bad. I quite enjoyed most of the funny moments. It's just not a movie I'd label as a comedy, but more of a feel-good movie. And I believe it would have been an even better movie if they tried to write a feel-good movie.
That or just cast someone who isn't Will Ferrell. I don't know but seeing Will Ferrell in this feels unnatural. he just doesn't work in this movie in my opinion, he and the lead actress just don't have the chemistry needed for this movie.
In conclusion, cast someone who isn't Will Ferrell for this kind I movie.