Silent Hill 2 and God of War both have the same rating of "Mature" on the box, and both of them feature gore and some sexual imagery, but there's a world of difference in their attitudes toward them. Age of Conan is one of the few triple-A MMOs to really try and tackle mature content in the field as a selling point, with most of the market leaders eschewing it altogether.
On the one hand, mature content opens the door for more adult and immersive stories to be told. On the other hand, it can also be used for cheap shock value and lead to less maturity in storytelling. Not to mention that it can lead to some backlash for developers (as BioWare experienced not so long ago). Where do you stand on the issue? Do you want unmitigated violence and nudity in your games, with all the concurrent issues they can bring, or would you rather keep things at a lower key to avoid the slide into immaturity?