Wow, reading through these comments is pretty upsetting. Lot of unwarranted, borderline misogynistic ranting. No reason to feel threatened, guys. Girls just wanna have fun.
Anyway, some observations about how women are portrayed in games:
Male protagonists dominate the top games, while female protagonists are primarily defined by their sex appeal (Lara Croft, Bayonetta, any female from Street Fighter) or are somewhat masculine themselves (Mass Effect's female Shepard, Samus Aran before she strips). In addition, many respectable female characters are relegated to sidekick status (Alyx Vance from HL2, Meryl from Metal Gear Solid) or become emotionally-wrecked villains themselves (GLaDOS, Aribeth from NWN).
For every non-mute (Sorry Chell), non-overtly sexualized, emotionally resilient lead female character, like April (Longest Journey) or Jade (Beyond Good & Evil), I can think of half a dozen females who always need rescuing by the boys: Princess Peach, Princess Zelda, Yorda (ICO), the Duke Nukem girls, and so on...
Based purely on personal anecdotes, most real-life girls I know gravitate toward games like the Sims, Oblivion, or World of Warcraft (PvE). Social chatting software like IMVU are popular among women too. I think in these kinds of games, they can define their own characters and their own place in the game world. They seem to like creating, customizing, and exploring, while approaching the content at their own pace.
That's not to say no women enjoy pressure-driven games like WoW (PvP), Starcraft, or Left 4 Dead--I remember at least 3 girls kicked my ass in separate L4D Versus matches--but the ratio of fiercely competitive girl gamers to guy gamers isn't very high, in my experience.
If developers want to attract more women playing games, I think they need to develop more characters that women want to play or characters that women can identify with. To do that, I would suggest hiring more female developers, writers, and play-testers. But that's a risky business move, and in this climate of conservative remakes and shooter clones, I don't see it happening anytime soon.