Season 5 of Diablo 3 is starting early next year, and Blizzard has detailed exactly what's involved in a new blog post. If you hated Seasonal Legendary items, you'll be pleased to hear that they've been done away with—while new Legendaries will be made available as part of the accompanying patch 2.4, they'll be gettable by all players, regardless of whether they've taken part in the season or not.
You will be getting new loot, however, in the form of Haedrig's Gift, a new bundle of Set items. Meanwhile, existing Conquests are being updated, while new ones are being added—you can read all about them at the preceding link.
Expect new cosmetic items, including cute wickle pets, wings and pennants, AKA those daft accessories I quickly toggled off while I was playing. Aside from the nixed Seasonal Legendaries, Season 5's biggest feature might be its Season Rebirth system, which will allow players to take non-Seasonal characters and "instantly transform them into a Seasonal character, ready to jump straight into the action on day one".
Season 5 of Diablo 3 starts on January 15 (at 5pm PDT in North America, 5pm CEST in Europe, and 5pm KST in Asia). So at 5pm, then.