Honestly the mechanics is what developer got right and their focus on them is what made the game stand out. For an action game the content isn't just one loop, instead several seamlessly interconnected scenes. Think of even the text based RPGs, the visual novels, most skip directly to the sex, and here even the enemies that go to immediately sex the player character have to go through insertion.
And the entire game's dungeon randomly generated dungeon becomes a set piece. There are no cut-ins, no premade cutscenes, or anything aside from organically generated moment to moment action. And such a erotic action game likely isn't going to found again. We were one step outside of Eden.
Though just to more coherently organize my thoughts. Fewer more well animated scenes are better, build tall. Don't make enemy characters and push them out with content as thin as paper. Make the action smooth as silk and don't skip scenes they build anticipation. And finally keep things in a theme be it fantasy, modern, futuristic. Even if someone wants something thrown in if it clashes with the convention or design for the setting TOSS IT. There's far to many porn games that will have been better if somethings were left out. (I.E., extreme fetishes, scenes that deviate or clash with the theme, and or enemies that are marginal.)
