Atlas of Worlds - A map for your maps, essentially. In one interview, Chris hinted towards you picking one of the 4 corners to start in, and working your way towards each of the endpoints in the center. For each endpoint of each corner, you get 1 key. Collect all 4, and you, presumably, have a showdown with the Shaper. There are 'pictures' inscribed into certain spots of the Atlas, intended to give hints as to certain drop locations for items. An example given was the new base helm, the "Bone Helm," which has an implicit Increased Minion Damage on it.
2 new currencies - Shaper's Orb, Cartographer's Sextant. A Shaper's Orb will upgrade a map's tier once it's set inside the Atlas. For example, using it on a Gorge inside your Atlas will up its tier. This is important to note because those new bases will be restricted to certain tiers. In order to get higher ilvls of said bases, you need to utilize this currency. The Sextant will randomly add another map mod to the map you use it on within your Atlas. The difference from normal modding is that it creates a red circle (similar to Threshold Jewels in your skill tree) which will affect any other nearby maps with the same mod. Any overlapping circles will apply both extra mods for some nasty shit.
2 new skills. Both of which have been hinted at utilizing the new 'channeling' system they added.
Very little skill nerfs, for better or for worse.
New uniques, of course.
Essence league. 20 different essences - some can only be obtained by corrupting your existing essences using the essence equivalent to a Vaal Orb. There are 7 tiers of Essences, with growing efficacy per tier. 3 of a lower tier can upgraded to 1 of a higher tier when vendored. Essences are found randomly in the world as a group of frozen enemies. These essences then modify the group of enemies to do nasty shit. Kill them, and get your essences. Essences revolve around crafting. Using one on a white item will grant you a rare item with a single guaranteed affix as specified by the essence. Some of the mods shown were high tiered life roll on an item of your choice, +15% chance to gain a charge on kill if used on a weapon, 15% increased fortify effect on an amulet, or % spell damage on a weapon.
Zana shows up after completing your first map.
30 new maps. Most of which seem to be focused on higher tiers.
Clearing each spot on the Atlas will provide a "100% increased special item drop rate" on that particular map in the future. Not sure if it means 100% rarity bonus, or something in particular.
Performance improvements. Multi-threading now actually works, it seems.
There will be another wave of press interviews coming shortly with even more information.