One of the problems you face when you're expected to create a more realistic game engine is that the amount of detail you need to supply increases quite a bit.  Most people don't care too much whether or not a tiny pixel character has a snooze mode, or if they gasp in horror when, say, their friend is being carved up by an especially resilient chainsaw.  But as we demand more of our games, details might not be important enough to put in.  To wit: