[This post continues from the already-available Part 1.]
The surface is the part which you perceive in the most immediate form and so superficiality refers to the way you comprehend things just by their appearance or its most obvious. There's a lot of content and functionality under the surface which exists wherever you look, and in fact there's always a lot happening in even the most still things. However all this deep stuff happening under the surface is hidden, it requires for one to analyse, study and meditate about what's going on to break into the different layers of depth.
A game designer is a person which should always try to know all the things that will be happening deep inside the game's experience. Nature has already got it going on with the layering idea, but a designer must think in reverse in order to achieve this same effect. The objective: keep the surface as simple as it can be exposing just the main purpose of the game whether it is providing fun, giving some relaxing moment or communicating and idea.
A good example on how to design a simple surfaced framework is a concept taken from object oriented programming (OOP) called encapsulation. Encapsulation is a property in OOP in which the code is separated in different classes of objects which are composed of a private and a public part.
The private parts hide all the inner functionality leaving only the public parts which are the relevant ones for other classes to use. A programmer who has never used an object of the specific class won't have to know anything about the functionality of the object, he only knows what the object is and what it can do.
Implementing OOP is equally useful in minimalistic design. The designer thinks of all the functionality and content that the game will have and then he exposes only the most relevant parts into the surface.
An example of this type of design can be watched in Sid Meier's Civilization change from Civilization IV to Civilization Revolution. Civilization games used to evolve adding more and more functionality and content in each iteration. It started from being a game where you just founded some cities in which you could build some city improvements and units for military, technological, cultural or commercial use with the objective to become the most dominant civilization in the world.
In Civilization IV you had the same game but you could manage religion, finances, politics, external relationships, a huge variety of resources, culture, pollution, technology and a lot more. Civilization got to the point where it was also used for education at schools and universities for its accurate simulation on the development of a civilization. The moment came and the design felt into the question: Is all this functionality really relevant for the player's experience? And the answer was Civilization Revolution. The difference between Civ IV and Civ Revolution is enormous: is like rewinding to the first civilization but keeping the most fun parts from its sequels and the cool graphics.
Some people (like myself) still likes more the complexity of the previous Civilizations. Complexity is something really attractive to people who likes having the depths of a system the most exposed as possible for manipulation. However simplicity is more appealing for the joy of being and having fun which may be the purpose of most games.
But there's a catch to simplicity: it is difficult to achieve correctly. Simplicity must be balanced and find equilibrium between the parts it is trying to simplify. Simple is not the same as shallow or empty. Depth still exists in simplicity and represents the most important part of all of it.