The baseline world, Masor is a "generic fantasy world". It has the core races in their most basic forms (high elves, hill/mountain dwarves, etc), and functions the most like the default assumed in the PHB. If Masor was said to have a theme it is fallen magical empires. Masor was the center of the Pnakostic Empire, and has had several empires rise and fall since then. Another theme is the of the central world as it is the closest to default and most likely to be used in the case of varied backgrounds. Even its climate is the closest to the default. Masor does have an odd trend in temperatures where unlike the other worlds which cool as you approach the northern reaches of the Southern Lands, Masor warms as you do so. This is because of the excess magical energy in the Badlands turning into heat. This means that of the region on the map, about 4 grid spaces down is the coolest region, though most of the map is temperate with the exception being the Badlands themselves which are Warm.
Dominated by the Hallowed Empire, Alli'ur is a drier world than Masor and a warmer one. Alli'ur is inhabited by great reptiles, dinosaurs that have been lost on Masor or Hondaro, and has the highest population of dragons. Much of Alli'ur is wrapped up into two major factions, the Hallowed Empire and the dragon armies of Gilgast the Red. While only border wars have begun thus far, neither force ready to risk everything in full-scale war, the two know that sooner or later war will begin in full. The Hallowed Empire itself is ruled by a great wyrm gold dragon, known as the Hallowed Emperor, who initially built the Empire over a millennium ago by carving it out of the lands controlled by the orcs. The Empire has since stretched beyond even its own ability to control and even with the aid of the most powerful wizards and priests of Alli'ur the Empire is growing too large to maintain efficiency and honesty.
The Hallowed Emperor once won over countries by granting aid, and the example of prosperity within the Empire. Now new countries enter due to need for that aid, need for that protection, and such aid is withheld from non-member states. Once the Empire seemed poise to stretch into Masor and challenge the corruption rising in Toyama, but now the Emperor has begun to order even private interests away from these areas. Part of this may be age, even for a gold wyrm the Emperor is old, part of this, though, is that the Empire has already expanded to the limits of his power to maintain and with full-fledged war on the horizon resources must be focused towards it and not vain attempts to expand control into other worlds. The Emperor has not, however, turned away from diplomatic dealings with these worlds and many forces realize that should the Empire fall Gilgast's hordes will not stop in Alli'ur and will not assimilate new regions peacefully. Should the Empire fall, Tiamat's forces will sweep across the Three Worlds and the Age of Heroes may end as nothing more than the precursor to the Age of Dragons.
Even so not all of Alli'ur is the Hallowed Empire. Near the southern coast is the lands of the coast elves. They are a culture, or perhaps subrace, of elves lost since adapted to a life at sea. They are not aquatic elves which swim, through the depths, but a proud culture of sailors, merchants and explorers. Lizardmen are also common in these southern regions, they are the wetlands of the world, including vast marshes where Masor has plains.
Hondaro is warmer and wetter than the other two worlds, covered in lush rain forests and wet lands. It is home to hengeyokai, kurobokuro, vanara, and its spirits have a closer relationship with mortals than those of Masor and Alli'ur. Its arcane magic, however, was stunted as the Nishano Empire rose up and overthrew the Pnakostic Remnant soon after Pnakost's disappearance. This not only means that the common tongue on Hondaro has changed unrecognizably compared to that of Masor and Alli'ur where the Pnakostic Empire stood for at least a thousand years longer, but that much arcane magic was lost. Arcanists of Hondaro traditionally turned to the spirits, augmenting their arcane powers with spirit guided gifts at the cost of obeying certain taboos. With the reopening of the Gates and Bridges, and ease of travel between the Three Worlds in the current era such magical knowledge has transferred easily.
Hondaro, like Alli'ur, is largely dominated in the South-West by a single empire. Where Alli'ur's is a coalition of allied states under the guidance of a single ruler but with each state maintaining a large degree of autonomy, Toyama is an isolationist regime where even transport of ideas and skills internally within the empire is restricted. Toyama operates under a strict feudal class system with a heavy emphasis on the warrior class.