Patch 2.1.0 promises the first significant content patch to Diablo III since the launch of Reaper of Souls, and Blizzard has finally blown the lid (officially) off on what this patch will deliver. Seasons, Legendary Gems, Leaderboards, and more are detailed in the First Look post that went up today, which you can view on Blizzard's site now.
Obviously Seasons are a big deal, providing the much requested ladder-like function that fans loved in D2. Lots of details revealed in the post on Blizzard's website, including confirming once again that Legendaries and Paragon experience points will dovetail into your permanent characters once the Season ends. Season-specific Legendary items will also become part of the standard loot pool once Seasons end as well.
Legendary gems sound like neat additions, and it will be interesting to see how powerful these things can become. Allowing them to be only socketed into rings and amulets means you'll be giving up valuable space on those items, typically Critical Hit Damage, Chance, or Primary stats, so here's hoping those gems can compensate for those losses nicely.
Also, the changes to Rift Keystones sound great, with the requirement to open a rift going down from 5 to 1 being a fantastic and much needed change. Greater Rifts should be fun, and provide a solid challenge for those that have been farming Torment VI for months now. And I know a number of Monk players will be pleased with the change to Dexterity granting armor now instead of the oft-useless Dodge stat.
Check out the details over at Blizzards "First Look" page here: First Look: Patch 2.1.0