One of the hardest things about writing video games is designing them. Sure, 3D mathematics is hard, but thinking of a fun game and a design to go along with it is just as difficult, in a manner of speaking, and definitely as important. Who cares if you have the latest volumetric photon traces if the game sucks?
Now, thinking up a game idea isn't that hard. It's the details, final implementation, and visual look that make the difference between the bargain bin and the cover of PC Gamer. So let's outline some basic concepts and rules of thumb that have worked for me and paid for a Dodge Viper or two.