I told one of my buddies that I was going to write about Fantasy General, an outstanding fantasy wargame, but I decided not to. You heard me!
Instead, I'm going to write a little about classes and how they shape the default setting of our campaign world by explicitly expressing what is and is not possible to player characters and why.
As a quick example, we all know about the Magic User of OD&D, or basic D&D. He has a finite list of spells that he can perform, and that is the extent of his magic. He can shoot lightning bolts across a room but cannot generate an electrostatic charge. He can put a man to sleep but cannot awaken him again. He can turn a man to stone but cannot simply encase him in stone. The Magic User is a man of no subtlety, a man who wields the forces of magic with all the grace and finesse of a sledgehammer. And this sets the tone for your campaign.
One of your player characters (or maybe more) has this small set of incredibly destructive magic and, as they say, when you've only got a hammer, everything looks like nails. Suddenly every encounter is a chance to scour the earth with flame and explosions, every diplomatic encounter is a chance to command another's mind. And you wonder why the players always fight to the death!
It's really not just limited to magic. The class features are the number one game-defining decision. If you have a game where you choose one of four classes, you have a game of specialists with role protection. If you have a class-building system, or a "buy what you like" system, then you have a game of generalists where the idea of "role protection" is a little laughable.
Let me give a quick example, and then I'm out of your hair:
Imagine you're playing D&D, except that your DM hands you a little handbook and says, "I'm trying something new. Instead of the classes you're used to, we're going to use these classes." Inside the handbook, it explains that the Fighter is now a graceful Dervish, who is quick-footed and nimble. The Cleric is now a Blood Priest, who has no grasp of holy magic but heals and harms through an understanding of the magic of blood. The Magic User is now a Runemaster, who casts no magic but utilizes the power of Runes, which consist of enchantments laid on objects and people.
Your game has changed enormously, obviously. You no longer have anybody wearing heavy armor. You don't have access to light spells (since it would normally come from the Cleric, who is now limited strictly to healing and damage spells. Your Magic User has no gross magical powers- instead, he creates use-limited magical objects that he can hand to others.
And as obvious as it is that the game has changed, it makes me wonder that more people don't inspect the impact of the default player classes in their games. If I had a dollar for every time that something in a default class simply smashed the default assumptions inherent in any game world, I'd be a very, very rich man.