Caution: What follows is extra-fluffy because I changed just about everything, and it's tricky to write out for me unless I'm trying to make it interesting to read. My rules set is more "d20" than "D&D".
Excepting the Endless (a "male" solar and "female" lunar power, the quiescent spirit of nature, and Death), the gods are small and physical. The world is infested with spirits and "dual-natured" creatures (physical creatures with inherent magical power), and some are worshipped for their power in the mortal world. From this worship they draw more power, and those whose worship is common in more than a single city-state can carve a personal realm in the Ethereal. These gods do not grant spells; "not razing your village" is sometimes all the reward they offer for the sacrifices provided to them.
All magic is of the same source, and anyone could learn to tap into it (EoM:ME
rocks); some sorcerers are independants, some rule cities, and some serve in the temples of powerful spirits.
Primarily the human civilizations spread across two continents possess early Iron Age technology, but they and the Idwali (a related race, Small, taking the place of halflings and gnomes) are the heirs to a cultural, technological, and magical heritage that makes Exalted's First Age look a little primitive and superstitious. Of course, what little they have uncovered of the legacy of the Ancients is either utterly inscrutable or phenomenally dangerous.
The dwarven holds, linked by the Labyrinth (a bizarre, ancient network of tunnels a hundred or so feet below the surface) hide
massive steam engines in their depths. These are not for powering mine cars or automatons; they are used to dredge underground seas, run a disposal belt to carry slag miles from their homes, and open surface gates that half a hundred giants would strain to move; a single piston or cog would require a dozen strong men to move into position.
The two breeds of elves are, by sorcery and martial skill, the dominant power of the known world, assuming they could somehow be roused to war. The Dawn elves, dwelling in a forested demiplane physically connected to the Worldroot Forest, are drunk on too much time, too much prophecy, and too much arcane power to take more than peripheral notice of the world around them. The Dusk elves, hailing from an island cluster to the southwest, are sailors and elementalists without peer, but their souls are at sea even with their bodies on land. They appear content to smash the hobgoblin raiding fleets and sail into the massive elemental storms of the Landless South, virtually ignoring even demands from the Elvish Deliberative, the entire race's ruling body, until it suits them to return home.
The hobgoblins, known to most of the world as the kul (and yes, it is from their culture that human language has drawn the world "cull"), are fashioned into a nation by their Tyrant, a god/spirit that walks among them. While they dwell in an unenlightened, militaristic, slave-driven hydraulic despotism, they are second only to the dwarves as engineers, particularly where warfare are concerned. In fact, the first true sewers were fashioned by the kul to make their cities better able to endure a seige.
The giants were once Titans, beings of raw creation and might. When they overthrew their gods they were cast down to the lesser beings they are today. Before this, so great was their power that their first efforts in craft, war, and sorcery spawned whole races. When a Titan first struck one rock against another to make a tool, dwarves sprang from the chips that flew; when first they hammered copper with stone to make a blade to kill with, orcs sprang from the sparks of the forge; when first they carved a mystic rune in stone, the stone removed from its design sprang into a living being. These legendary people, even if the story is true, are unknown to the current age.
The orcs are a people of elemental earth and fire, more magical creatures than mortals, locked in endless war within the Labyrinth against the dwarves. This is more than a sort of ancient sibling rivalry; orcish corpses burn hotter and longer than any other substance, and are used to power the great forges and engines of the dwarven holds.
Goblins are a Monstrous Humanoid, superficially similar to their Monster Manual origins but adapted to their environment; in the great southern jungles their arms are twice as long, with two elbows that each have full range of motion, while marsh goblins have gills, crocodilian hide, webbed hands, and a bacteria-infested bite. Each tribe is then further changed by their patron, invariably a spirit or spirit-creature of cruel nature.
When people speak of dragons, they do not mean anything like the color-coded disposable entities of D&D. While there is a gliding, firebreathing being that men call "dragons" and rarely grows larger than a bull (Discovery Channel, anyone?

), these are of bestial intelligence and primarily just predators with a curious natural weapon. What they mean are the Dragons; massive entities born of sorcery and power, like a piece of raw creation given wings and scales and an appetite for treasure. They do not breed (thank the gods), and it is unclear if they spring from or create situations of great energy; titanic wars, perfect storms, volcanic eruptions, hurricanes that last days and tornadoes two miles across at their base have all evoked a Dragon unique to that event. They are the ultimate energy consumers, mightier than the gods and spirits of the world, and largely unconcerned with world events. However, they are arrogant beyond measure and have forged a single unified religion among the mortal races; any Dragon with an individual cult invariably had that cult smashed by its jealous siblings. The Dragons do not force this worship on others, but some of their servants do out of a fear of divine punishment or a belief the Dragons will "burn the world clean". The idea that mortals could slay a Dragon is laughable - but it is a laugh tinged with fear, as some sorcerers believe their death would have catastrophic effects.
There are probably 10,000 more paragraphs I can write like that to provide my world's flavor, but I should stop now. You get the idea.
Also,
AFGNCAAP, I'm using the generic classes myself; any chance you'd be willing to put your NPC class up in House Rules, and maybe a couple of the redesigned prestige classes? I'm still working on the crunchy parts and I'd love to see someone elses' approach. Plus, the less crunch I have to balance the more fluff I can spin.