Per noism's post over at his place, I rolled up five random monsters from the Labyrinth Lord game and then envisioned a campaign world where those monsters are the dominant intelligent races.
My building blocks:
Bats, Giant
Goblins
Gnomes
Hobgoblins
Wolves
The game world is a medium-to-small continent running from east to west -- imagine South America from Argentina to Tierra del Fuego rotated 90 degrees clockwise. The vast majority of the land is grasslands/steppes, roamed by the Hobgoblins and their Khans. Nomadic horse-riders with few fixed cities, they drive great herds of lifestock from grazing to grazing land while setting up extensive tent-encampments. When they're not engaging in various wars of succession, they raid...
...the walled and many-domed cities of the gnomes. Naturally magically proficient, the gnomes have used their abilities to create complex stone cities lorded over by the gnomish aristocracy. These small and dense fort-cities, filled with constantly-backstabbing guilds, are mostly located near the coasts of this land, all of the construction being done by golems and other magically-created constructs as well as partially by...
...a slave race of goblins, who also serve as the main agricultural workers for the gnomish cities, with golems as their overseers, and who populate the slum tenements in the cities themselves. There are a small amount of free goblins, both those who live in the cities as adventurers and in scattered wilderness communities, most of which are in remote and inaccessible locations, hidden away from their mounted cousins, although their proximity to the great northern mountain range leads to conflicts with...
...the clans of the wolf-men, whose jarls chafe under the leadership of their King, grown old and infirm. The refocusing on internal politics means that the gnomish cities and hobgoblin tent encampments have been largely free of the raiding parties that swirl down from the craggy peaks like vicious snowstorms. Most wolf-men are hunters. Those wondering what machinations are taking place in the wolf longhouses and hill-forts would be best advised to seek the knowledge of...
...the bat-men, whose great underground settlements are not easily found and whose wizards surpass even the greatest gnomes in knowledge of the secrets of this world, many which lie in the lightless caverns the bat-men frequent. Aside from groups living in the great caves of the northern mountains, there are rockier sections of the grasslands where the bat-men are said to spill forth like a great geyser at twilight from their cave entrances, their scouts scouring the land for anything foolish enough to be seen moving.
So. Hobgoblins = steppe hordes; Gnomes = magic-based nobility; Goblins = slaves/underclass; Wolf-men = Viking/Germanic clans that leave woods full of skeletons hung from the trees; Bat-men = mysterious underground race, nocturnal scourge of large areas, know the most secrets/forbidden knowledge.
I think all of the races should be playable in a red-box race-as-class system, with Gnomes and Bat-men being natural magic-users, Wolf-men and Hobgoblins as fighting men and Goblins fitting into the rogue niche. I'm not entirely happy with Goblins, as they don't fit into either the crazed maniac goblins of the Warhammer universe or the fey/stealin' babies fairy-tale creatures that I generally like to have them as; however, they do work best as the Short, Nasty and Brutish creatures of this world -- also worth noting that there's no "pleasant race" here, the Gnomes are probably the closest; I envision them more as the entitled gentry, interested more in embarrassing their rival at the next society do and creating various golem-like creatures to dominate their slaves -- any playable Gnome would probably be a trader's son or somebody on the lowest possible rung of Gnome society.