You would probably expect me to start talking about Charles Dicken's novel Great Expectations, but I won't: What I've been wondering about lately is the power of toying with the player's expectations, sometimes giving them what they want, but othertimes putting a twist to the experience. You set up a pattern, kill end of level boss = get reward and go to next level. This happens three times over. The fourth time, the boss starts an explosive timer, the base is going to blow up. So the player has to fly out of the base really quickly and avoid the falling debris. nat_loh talks about patterns in this thread http://www.igda.org/Forums/showthread.php?s=e3ca99ad9fc55faacdfed7ca79808fcc&threadid=15696&perpage=15&pagenumber=1 Further more, I believe that this kind of pattern recognition can be extended to "MOOD and atmosphere", for example if you are walking through a child's playground you might expect it to be happy and fun (well, okay you might actually expect it to be filled with dangerous junkies syringes depending on where you live). If you find that the playground exists but no-one uses it because they are scared of all the drug-dealers, perverts and thugs that live in the neighbourhood then this might make you feel "sad", especially if it used to be a really nice neighbourhood. Any ideas on how we can work with this?

Difficult, but powerful. Part of game playing is learning, which requires some kind of reliability (with variety, mind you). You can certainly get a lot out of narrative expectations, along the lines of the old adage "there is only one plot: 'nothing is as it seems.'"

But when you extend this to gameplay, I think you start asking for trouble if it renders useless all that the player has learned up to that point (for instance, suddenly having the end boss be in a zero-G chamber, when you've never been exposed before).

OTOH, I've seen your boss example done countless times (again, though, the player has had a chance to acclimate themselves to the change in expectation).