
Season 17 (The Season of Nightmares) launches today simultaneously with the latest Diablo III patch. There are also legendary item updates, new levels of Torment, and a host of quality of life changes along with a ghoulish Seasonal buff!
The other great news is that Diablo III Season 17 players will benefit from the Set bonus provided by the previous season's Legacy of Nightmares. In other words, all can enjoy the advantages of the "no Set" Set and all Ancient Legendary you come across becomes a lot more valuable.

Any classes with particularly strong Legacy of Nightmare builds will have the ability to test new combinations, and especially combinations focussed on the Ring Slots.
At the same time, classes that have historically relied extensively on survivability from their ring slots, will have more leeway to test building-altering Legendaries that don't depend on a given Class Set.
In a first, Blizzard are re-introducing legacy Seasonal Rewards for players who might have missed them the first time. Awards that were previously exclusive to Season 5 will become available to Season 17 participants who progress through this Season journey.

Also, as well as the Pants and Boots slots of the select, Conqueror Set, Diablo III participants will be able to gain a series of portrait frames based on the ghoulish Greyhollow Island.
For pet collectors, in Season 17 you will be able to add the scary but cute Wickerman to your collection.
Players who complete all nine chapters of the Season Journey will be rewarded with a new cosmetic item, which means the Galactic Wings could be yours!

For people in a hurry, the Sprinter and Speed Racer characters return in this season, challenging you to complete all 5 Acts of the campaign in under 1 hour. Greedy Nephalem might be more suited to completing Avarice or Avaritia, where you'll need to rack up a gold streak of 50,000,000 outside of The Vault. The Thrill and Superhuman request that you complete a Greater Rift Level 45 without the assistance of any equipped Set Bonus. It'll be a Season for alt-aholics, as Years of War and Dynasty requires completing a Greater Rift Level 55 with the set bonuses of six different Class sets, while Masters of the Universe and Masters of Sets ask you to complete eight different Set Dungeons.

If you complete Chapters 2, 3, and 4 of the Season Journey, you will be rewarded with three of Haedrig's Gifts. Each Gift contains a few pieces from one of your Class Sets. Players can only unlock one Class Set in this manner per Season across Hardcore and Non-Hardcore.
Here are the sets granted by Haedrig's Gift in Season 17:
First, three new Torment levels are added to the game, so that there's more variety and efficiency in farming for players deep in late-game content.

Higher Torment levels means more experience, gold, and Blood Shards, along with improved rewards from activities like Bounties and Nephalem Rifts. New search functionality added to the Stash (on PC only).

There are a few other small changes coming, such as an Expand/Collapse All button for recipes on Crafters (PC only), most Bounty indicators appearing immediately after entering the Bounty area, and Death's Breath now dropping from Horadric Caches. Season 17 is sure to be the greatest Season yet!