Most complex adult game you ever....

[RogueKnightUK]

Lab Rats 2 (link) - by a huge, huge margin. Nothing else is even close. Characters are generated on the fly, complete with variable stats and characteristics, a basic personality, a set of randomly generated likes and dislikes, fetishes and turn-offs that are partly dependant on personality type. It's a fully fledged, fully functional strategic resource management sandbox game that also happens to be a sort of 'slut trainer', and have a story ongoing.

 

[Socural]

Has accidental women been mentioned yet? That game takes the crown for me right now

 

[baoka]

Let Me In. You play as an orc trying to talk a princess into letting him into the castle. It uses primarily a point system of building trust/distrust and a text interface where the princess responds to your input. Without a guide, it is a pretty difficult game to win.