The Isle of the Thunder King is the new daily quest area in Patch 5.2, as well as where the Throne of Thunder raid is located. You used to be able to get there from a portal in your faction's capital in the Vale of Eternal Blossoms, but the most recent PTR build moved it to near the Shado-Pan Garrison in Townlong Steppes. The entire island is restricted to ground mounts only.
Upon arrival, you are in your faction's base, with daily quests and vendors. As Dave Kosak reminded everyone, many things could still be placeholders, as this is still the PTR.
In the Horde base, there is a quartermaster there for the new faction, but currently it is just Vasarin Redmorn as a placeholder, as well as Aethas, and some other familiar faces. There is also a portal back to Shado-Pan Garrison.
Over in the Alliance base, you find the Kirin Tor, The Silver Covenant, Jaina, and Image of Archmage Vargoth, along with some other familiar faces.
After picking up your daily quests, you cross the bridges to the main island area. On your way out, you can grab a 60 second haste increase and power cost reduction buff from one of the Mana Collectors. This area is guarded by Silvermoon Spellbreakers and Sunreaver Constructs.
Throughout the island, there are several rare mobs that can drop a stone
that is used to summon a mob that requires a group to defeat. You can
also find the stones in the various chests that spawn across the island,
similar to the Ancient Guo-Lai Cache.
The center of the island is the Diremoor, which contains several types
of quest mobs, including a wandering Devilsaur and mob in the center
building to kill that are quest objectives.
Moving further north, you will find the area that is outside of the
Throne of the Thunder King. It is also used for questing, as well as the
new world Boss, Nalak.
To the west of Diremoor is the Court of Bones, another questing area.
Several scouts from your faction have been captured and kept prisoner in
The southwest corner of the island is Trolltonshire, a questing area
with trolls! Be sure to watch for circles on the ground that mark the
constant bombings from the Zandalari Skyscreamer flying above. You can
use the Zandalari Potions that are sitting around the camps for a buff
like Jaguar Ferocity, Jaguar Speed, or Jaguar Stalker.
The southeast corner of the island has been taken over by the Saurok,
and questing there gives you a Saurok disguise that allows you to run at
ground mount speeds and jump much higher and farther than normal.