For many, Deus Ex is the greatest video game ever made. Its design is as open ended as any video game that succeeded it, even 15+ years after its release. In fact Deus Ex is still ahead of its time -- it did things that most modern games aren't ambitious enough to attempt. Now, in a blog over at Games Industry International, Warren Spector has put together the design rules his team worked to whilst creating Deus Ex. Its fascinating.
I won't list them all here, since that would be a disservice to the original blog, which you can read here but I do like this one, particularly because it seems like I spend half my time in games these days watching someone else do something cool.
Players Do; NPCs Watch -- It's no fun to watch an NPC do something cool. If it's a cool thing, let the player do it. If it's a boring or mundane thing, don't even let the player think about it - let an NPC do it.
Yes Warren, yes. Preach.
Warren Spector's Commandments of Game Design [Games Industry International]