A presentation by Nick Fortugno was made on developing games. He explained how the difference between hardcore games and casual games is on the simplicity vs. complexity of the game. Differentiating on how difficult they are to learn.

A casual game must therefore have a simple set of mechanisms to attract the gamer, a set of mechanisms that are:  Easy to learn, but takes a lifetime to master.

But the casual gamer wants to be challenge and the games need to vary to keep the gamer’s attention, which is why the use of terrain will be of great use. Below is a few slides from the presentation, where an hardcore game is being used as an example.