Men and women are dissimilar in the ways they think, act, and react. This dichotomy starts with the brain. Female brains are more connected between the hemispheres, and male brains are more connected within the hemispheres. Without getting too technical, this means that women tend to view the world holistically while men tend to view it through a more directed lens. This inherent gender difference influences almost every aspect of life, including sexuality.
In the bedroom, this distinction between the sexes manifests in two primary ways:
Among women, emotions and interconnectivity are seen as valued parts of the sexual act. Among men, feelings and connections are viewed as potential roadblocks to the sexual act.
This is most likely an evolutionary development. Over the centuries, men have been conditioned to "spread their seed" as widely as possible, to perpetuate their lineage. Meanwhile, women, who potentially face nine months of pregnancy, the pain of childbirth, and many years of child care, have had to think about things like whether a man will stick around long enough to help her out, how he will treat her and her child/children, what kind of provider he will be, etc.
Of course, these evolutionary imperatives are pretty meaningless in the modern world. The human race will not die out if a man doesn't procreate, and women today are perfectly capable of surviving (and thriving!) as single mothers. But thousands of years of conditioning are not so easily discarded. Our brains are wired the way they are wired, so we act the way we act.
Women tend to objectify a partner's character traits and/or their emotional connection with that partner whereas men tend to objectify a partner's sexual body parts.
Needless to say, this is related to the evolutionary imperative discussed above. Men are programmed to want sex; women are programmed to want a relationship. And this is very deeply ingrained. Even physiological arousal looks different for the two genders. For instance, in a well-known study, men and women were shown a series of romantic and erotic images. Responses were measured both subjectively (by what the test subjects said they felt about a particular image) and objectively (by a plethysmograph, used to measure blood flow to the test subject's penis or clitoris).
Men's responses were highly gender specific. Straight guys responded to naked women and heterosexual intercourse; gay guys responded to naked men and homosexual intercourse. Meanwhile, two-thirds of the women displayed gender-neutral responses. Instead of being turned on by a particular gender or by gay/straight intercourse, they responded to imagery that depicted or at least hinted at an intimate connection.
No, not every person (male or female) falls into these easily defined categories. However, most males will at least lean toward being more visual and visceral with sexuality while most women will at least lean toward being more relational.
Use this insight to inform your decisions when it comes to dating and sex. Just because you are subject to biological imperatives doesn't mean you always have to act on them. Use your logical brain to synthesize what you know about your evolutionary tendencies and the realities of your life to make the smartest choice for yourself. What will make you happy in the grand scheme of things? The answer to that question should inform your relationships far more than your basic biological instincts. Seeing the whole picture is the first step to designing the life and relationships you want.