I think that the height of game design lies in the designers ability to give the player the freedom to choose how he approaches the game, and nevertheless the player still gets a specific and intended experience.
There’s a moment of perfect game design in Diablo (by Blizzard North), and it is has to do with the Butcher.
When you first start playing Diablo, you’re almost guaranteed to get the Butcher Quest. It’s your first quest and it’s your first boss battle.
The Butcher’s room is unique. And when the players first encounter it they can immediately tell that there’s something special and foreboding about this room. The room is on the second floor (very early in the game) and its isolation, design, and bloody, gory props are completely different than anything the players encountered so far.
They’re almost guaranteed to make the connection between this room and the Butcher Quest. They know what they will encounter behind the door to this gut strewn place.
Already this is pretty good game design. But this is where the design of this boss battle becomes ingenious:
At this point, there is no possible way that players can beat the Butcher.