In your opinion, what makes a good love story?

In my story, there is a young girl who meets a unique young man, and over the course of their lives they become close friends and then lovers in their adulthood; however, the story doesn't have a typical happy ending. I am curious, what makes up a truly good love story? Do you prefer vampirey, gushy, Notebook-esque romance, or long, beautiful stories of two people who fall in love over time through war, fights, and loss?