The title of this movie is literally what it is: he said, she said. If you look closely at the credits the movie has two directors and two writers as well as two leads for a reason.
Basically the movie is two mini-films telling the same story of a couple meeting, competing, coupling, and spliting twice. The first half centering on Kevin Bacon was written and directed by men and the second half, centering on Elizabeth Perkins was written and directed by women. Not only do they use the same basic plot, but they use the same scenes, each shown not only from the POV of a different character, but a different gender.
Each mini-film alone would be a passible romantic comedy, but what makes the movie really work is the contrast. After seeing his side: what was important, what was stupid, what was good, what was bad we see hers and realize how something that is absolutely nothing to one is the most important thing in the world to the other. Most importantly the differences reflect generally common wisdom on the topic. Once has to ask if this is intentional or the natural byproduct of the differences between men and women.
Bacon is, as usual, himself (Kevin Bacon, much like John Wayne, plays himself in most movies and certainly the ones where he is at his best). However, the everyman Bacon is the perfect choice for this role. Perkins is very good as the self-assured but still vulnerable woman from the first generation of post-feminist revolution career women who has feet in both the feminist (career) and pre-feminist (marriage and family) world. She is as fully realized as her later sisters such as Ally McBeal and Bridget Jones.
Add in Sharon Stone as the tramp (and a more interesting one than Basic Instinct for my money) who realized she was in love but too late, Nathan Lane as the perfect mix of caring boss, and stir in good writing in pacing and the result is a funny and insightful romantic comedy and an above average movie.