Detailed patch notes are not yet available, but here's a first look at the new module, now on Preview as of 2019-12-12.
Feedback threads so far:M18 DungeonM18 Class Balance AdjustmentsM18 Zone, Repeatable Quests, and Heroic EncountersM18 General
Some notable features, this module:New storyline: Descent Into Avernus
Join us in a devilish new zone! This new storyline also includes new Heroic Encounters, a new campaign, and new rewards.World Map update
We've given the World Map a less-cramped treatment, with tabs instead of magnifying glasses for traveling between the Sword Coast, the Underdark, Chult, and beyond.New Dungeon
Unlocked by the campaign, this dungeon provides an epic experience, and is a step above the 5-player dungeon, Lair of the Mad Mage, in difficulty.Class balance changes
See the linked thread
for details and to give feedback; we're working on tweaks to help with player concerns about viability.
More info to come!