Since we're all describing settings, it's about time I unveiled mine.
[INSERT FANCY NAME HERE]
It's set in a medieval/steampunk setting, with extravagant cities and diverse locations. Around the world are eight temples, each built in order to enshrine the greatness of the eight elemental warriors.
Before I get into classes, I want to balance and verify the main feature to this campaign: the element system. When you first create your character, you choose one of four elements to represent the magical abilities of your character. Obviously, they're fire, water, earth, and wind. As you fight, you gain elemental EXP along with regular EXP, which grants you new spells and/or spell-like abilities, and eventually allow you to move into a new class of attacks, or a sub-element. The tree goes as such.

- Chart tiem!
- Elemental Chart.jpg (66.64 KiB) Viewed 1939 times
This is obviously a rough schematic. Notice these are four of the eight elements I described before. That's because light, darkness, force, and time haven't been included yet. Here are descriptions are the elements and their sub-elemental classes.
Fire: Attacks that often have strong power, but are in a concentrated area. Common after-effects are burning and asphyxiation.
->Smoke: Generally does no damage, but instead spreads malicious effects over wide areas.
-->Fume: An expansion upon Smoke. Includes damage in the equation.
->Magma: High damage output and high energy cost. Often destroys armor.
-->Volcano: An expansion upon Magma. Massive damage, extraordinarily high energy cost.
-----> Sol: Apocalyptic fire. Keep away from small children.
Water: Draws upon nearby moisture to lower energy cost. Arid areas require more energy, etc. Generally low damage.
->Ice: Freezes nearby moisture. Can immobilize enemies.
-->Mist: Spreads beneficial effects across a wide area.
->Vapor: Generally no damage, impairs enemy's abilities.
-->Geyser: An expansion upon Vapor. High damage, massive disorientation.
-----> Neptune: Ever wondered what Noah felt? Yeah.
Wind: Often hits multiple enemies at once, at a medium rate of damage. High energy cost.
->Lightning: Chain attacks for massive damage and stun!
-->Current: An expansion upon Lightning. Channel effects and damage through multiple enemies.
->Dust: Wide-area moves with virtually no energy cost. Often does little to no damage, but causes asphyxiation.
-->Debris: An expansion upon Dust. Adds damage and a higher energy cost.
----->Thor: THUNDER! THUNDER! THUNDER MAGIC, HOOOOOOO!!!
Earth: Low energy cost coupled with high damage and low range.
->Plant: Grow your own, or use them to suffocate things.
-->Nature: An expansion upon Plant. Or, suffocate things with trees instead.
->Stone: Bolster your allies or deal damage in the form of rocks.
-->Metal: An expansion upon Stone. Bolster your allies MOAR or deal MOAR damage in the form of metal.
----->Atlas: Ever thrown a mountain at someone? Yeah.
Q&A:
Q: So, how does this all work together with my class?
A: There are only three classes. Melee, Ranged, and Magic. Each one has skills/spells catered to the player's elemental path. For example, a Warrior would learn Fire Slam as a first skill instead of Fire Ball like a Mage would.
Q: THREE CLASSES?! WTF?!
A: Don't worry. Your class bears little to no meaning on your character. The class is simply a representation of your weapon set and class skills, each character can gain a weapon proficiency or the like and become a more specific fighter, such as a Swordsman or a Crossbowman. Mages can use more than one element to diversify their class. It works sort of in a Fallout 3 style where your actions with your class eventually narrow it down.
Q: Fine. How does elemental EXP work?
A: Killing things gets you elemental EXP. As you gain more, you unlock new abilities/spells until your element levels up. When this happens, you choose a sub-element and continue gaining elemental EXP. Your previous elements will gain EXP along with your new one, so, for instance, if you leveled up your element from Fire to Magma, you would still gain Fire attacks until you've learned them all as well as gaining new Magma attacks.
Q: This system sucks.
A: I know. I'm working on it.
What is the true path to victory? I say start with Flashman's stage.