Each era, and indeed many time periods within each era, can be adapted for a different style of game. The first and second era are intended to be times of myth and legend, the give the world history and depth. The third era is when the fun starts.
Early Third Era
The early third era is a time of exploration and omnipresent danger from the magical forces of Asmythe that nobody understands and nobody can control. Adventures are focused around survival, exploration, and learning the mysteries of Asmythe.
Delvers and sylvani live separately, never interacting with each other but striving to survive as best they can against the beasts of Asmythe. Humans and goblins have just arrived and, for the most part, live in different parts of the world and are attempting to build their own empires. When humans and goblins have any magical ability at all, it is wild and uncontrolled.
Mid Third Era
The mid third era is a time of magical research and defending against environmental hazards such as beasts and monsters.
In the mid third era humans and orcs have expanded their empires through most of the world. The Armada empire is expansive, but inexperienced and corrupt. Encounters with delvers and sylvani are rare, but trade routes with them exist in some areas. Magic is mostly understood and schools of magic teach and regulate magical practice just as the empire tries to control territory and the trading companies try to control travel. Environmental threats are kept under control by housing everybody in walled cities at night and deploying armed patrols during the day. Where human and goblin territory meet there is open war between them. A few subspace portals have been discovered among the ilthura ruins, but it is a mystery nobody understands and everybody fears.
This time period ends when Fealltor discovers necromancy and attempts to overthrow the corrupt Armada empire.
Late Third Era
This is the time period is most similar to familiar worlds like those presented in DnD, Pathfinder and where most games will take place. Humans, orcs, delvers, and sylvani territory press up against each other; peacefully in some places and violently in others. The Armada empire has rebuilt itself but leaves most human kingdoms to fend for themselves outside of Altazar. A few mages practice golemancy in secret. The practice of delver alchemy and sylvani druidism are spreading, but still very rare outside those cultures.
Adventures explore githxa ruins, enchant magical items, mingle with delvers and sylvani, and defend against goblins and beasts.
Early Fourth Era
The fourth era begin when, beleaguered by beasts and dragons, all four cultures agree to stop fighting each other and to rid Asmythe of beasts forever. In most places humans, goblins, delvers, and sylvani mingle freely and share knowledge. As the beasts are gradually eradicated cities grow beyond their walls and technology, both industrial and magical, grows quickly. During this time more subspace portals are discovered. Mages learn how to control them and begin to explore subspace.
Mid Fourth Era
This is a time of peace between races and and industrial prosperity. Subspace portals connect major cities across the world in an instant. The land is free from nearly all beasts, save the rare dragon attacks.
In such times adventure is political and devoted to discovering and stopping groups of ilthid worshippers and subspace death cults. Gothic horror games similar to Call of Cthulhu are best in this time period. Low-power superhero games are also appropriate in this time period.
Late Fourth Era
Things have gone badly for the people of Asmythe. Subspace rifts have opened and huge monsters, more powerful and more terrifying than dragons have come through corrupting everything they touch. The major cities have fallen but there is home. Magic and technology are now super powerful, perhaps powerful enough to fight and to win.
This is a good time period to play a post-apocalyptical and/or superhero game.
The fourth era ends when the supers are not enough and all of Asmythe is corrupted. Only then do the dagapesh awake and remake the world again.