Seasons, two new zones, and tons more content will be coming in the form of patch 2.1.0 to Blizzard's loot-filled title Diablo 3: Reaper of Souls according to a new forum post
Blizzard announced the new Seasons game mode back in June, along with details on the addition of Greater Rifts, a type of Nephalem Rift, and Cesspools, one of two new areas for Reaper of Souls. Blizzard's 2.1 Patch Roundup
revealed even more content coming with the 2.1 patch, including The Vault (another new area), leaderboards for Seasons and Greater Rifts, and details on the first Season's new items.
Community manager Tyvalir noted on the Diablo forums that while the patch only weighs in at 300mb, "it will be making several changes to the game files stored on your computer. As a result, the “Applying Patch” phase may take up to 30 minutes to finish once the patch has been downloaded." Those lost or wanting to catch up on the new changes can also find a stack of cliff notes giving the quick rundown on the patch over here