-There needs to be a reason why everything is so rapetastic, whether it's to breed or to drain energy or just religious purposes.
-Setting should probably be a mix of sci-fi and fantasy. Google 'Xenoblades'.
-Personal preference is that the playable characters are low-powered, and have a tough time fighting most enemies. They need to be smarter, or lucky, or else they get the dick/tentacles/captured/mind controlled/whatever depending on the enemy.
-There should be a reason why characters do not die or can escape from situations after the /d/ stuff is done. Perhaps a god/dess who looks out for those in peril (but his/her eyes are not always upon you).