Blue Valentine delivers on every level thanks in no small part due to its two incredible leads fantastically played by Michelle Williams and Ryan Gosling. Both display a wide range of emotions as the film went back and forth from their initial courtship to their relationship's eventual collapse. Saying both have "chemistry" would be terribly simplifying it since I believe they inhabited their characters so fully and so realistically that there are moments in the film when it started to feel a little too real.