Simple Complexity

I like the idea of layering 2-4 systems together to create a whole that is more complex than the sum of its parts.

For example, let's say we have a very simple game with four classes (Cleric, Fighter, Rogue, and Magician) and four backgrounds (Wilderness, Nobility, Urban, and Ecclesiastic). There are now 16 different combinations.

A fighter could be a paladin (ecclesiastic), knight (nobility), ranger (wilderness), or thug (urban). Instead of requiring four different classes or subclasses to represent those ideas, I've just layered two systems together. Another advantage is that the player is only confronted with four options at a time, instead of being faced with a list of 16 choices.

If we then layered on more choices (Offensive, Defensive, or Balanced, for example; or maybe Human, Elf, or Dwarf), we'd up the combinations yet again. At least 2 systems are needed to take advantage of this. More than 3 or perhaps 4 systems is perhaps too complicated.

ADDENDUM:

OD&D's layers (4):
- Ability Scores
- Class
- Equipment selection or spell selection
- Alignment

AD&D adds (5):
- Race (split from class)

D20 adds (8):
- Feats
- Prestige Classes (basically paragon paths)
- Robust skill system

4E adds (9):
- Epic Destinies

Plus each addition tends to add more choices within each category. 1E had more classes, plus ways to combine the base classes. 3E had yet more classes and even more loose multiclassing rules.

Where's the sweet spot? I think the Rule of 7 helps us out here: Perhaps 5-9 layered systems (erring towards the lower end) with either 3 components each (the Rule of Three) or 5-9 choices.

So if you have 5 "layers" with 5 choices per layer, that gives you 3125 possible character combinations.