I replied to this thread on another group where the exact same post was made, but since I doubt there is that much overlap between the two....
My gaming group that does the playtesting for my games etc has an exactly
50% split in players regarding basic Gender, so
My advice in this regards, for desigers, is to make sure that the game system gives an equal range of possibilities for characters of both genders. Also be sure to be prepared for folks that want to play characters of unusual gender and sexual status in the game. And expect this sort of thing to become important in the events of the game in all its varieties of romance and involvement, from one night stands to characters that are happily married to single parents.
I will note that from my experience you will find that women are more likely to want to play characters with unsual appetities and activities (crossdressers, bisexual, gay/lesbian, androgenous, fetishists, etc.) and that these will be important features of the character and how they will react. This may be because the women who I've encountered in roleplaying games tend to be more adventurous in this way in their own lives (and thus have a certain level of inner strength and a creativity that non-roleplaying women do) or because it makes it easier for them to seperate themselves from the role they play (a line of demarcation).
Women want a game to involve a lot more of the roleplaying aspects, a lot more intrigue, higher ethical questions, and general qualities of good quality fiction (everyone has a motive for what they do, no one is bad guy just because, there must be a psychological reason that makes sense). Combat should be fast and decisive, not something that takes an entire session to resolve. Women can be just as good at tactical and strategic thinking as men, but are not interested in such as a goal within itself in most cases.
An innovative and creative magic system that can be hacked at can also be a huge boon. A stagnant system (like D&D) where there are rarely any new possibilities, tends to bore them as much balancing the checkbook.
World color is important - a bland or predictable setting usually doesn't cut it. Lots of NPCs helps considerably in this way, as they will want to set up networks of contacts to interact with.