Rough summary, generally in the order they discussed but some parts moved to keep concepts together:
Subclasses at level 1 took away from class identity since you never spent any levels as just the class. This is being changed.
Warlock:
-Pact boon moved to level 1
-Subclass moved to level 3
-Pact magic replaced by spellcasting, no longer short-rest based
-They are half-casters as a base, but Mystic Arcanum is now an Eldritch Invocation so you can decide if you want to continue spell progression
-Mystic Arcanum also has <5th level options now
-Gaze of 2 minds - Allows you to cast spells from the location of the creature you are controlling
-"Contact Patron" feature added
-EB and Hex spell are now free with the Warlock base class (like Hunter's Mark for Rangers)
-Design notes in UA go deeper
-Flavor intentionally allows a warlock to have multiple sources of power throughout their story
-"Dark one's blessing" now procs when any creature within 5ft of you dies, you don't need to get the killing blow
-Patron spells are now auto-prepared rather than just part of your spell list
-Once per day, you can cast a patron spell without using a slot (like paladin UA)
-Class now gets Medium Armor training
Sorcerer:
-Subclass moved to level 3
-Level 1 "Innate sorcery", 2 sorcerer-exclusive spells, one is a cantrip "Sorcerer's Burst" that allows them to change damage type and has an exploding dice mechanic, "bread and butter cantrip"
-Other spell is Chaos Bolt
-Flavor is to show the unpredictability of innate magic, which was previously only shown via wild magic
-Metamagic moved to level 2, and pick 3 instead of 2, and can swap one each long rest
-All metamagics have been "revisited", with design notes for each
-Multiple other new features, "Sorcerer's Vitality", "Arcane Eruption", "Sorcery Incarnate", and "Arcane Apotheosis", "manifest as spells that the sorcerer will get for free, they are exclusive to this class because they again are all about the sorcerer tapping into their innate Magic"
-Sorcery Incarnate - Random number of sorc points back, "sorc version of rage", more than 1 metamagic per cast, advantage on spell attack rolls, possibly more
-Sorcerer's Vitality - Allows them to heal themselves
-Intend to make similar stuff on other classes (including martials) to help flesh out class identity
-New wizard-exclusive and warlock-exclusive spells added as well
Draconic sorcery:
-No longer need to spend sorc point to gain resistance to damage of your own type
-You can communicate with any "dragon" type creature, not just those who speak draconic
-New feature "Draconic Exhalation", interacts with Sorcerer's Burst cantrip making it AOE
-Draconic Presence removed based on survey ratings
-More features interact with the element you select
-Draconic Wings now interacts with Sorcery Incarnate, gives you wings during that, and adds an AOE to it
Wizard:
-Not as many new things as warlock and sorcerer
-2nd level feature "Academic" helps "when they're just using their big brains to figure things out"
-1st level feature "Wizard's spellbook" helps show all spellbook-related rules in 1 place rather than split up
-Spellbook can now be used as a spellcasting focus
-Feature also adds a new spell "Scribe spell"
-More new spells:
-"Memorize spell" allows them to change a prepared spell
-"Modify spell" allows them to change a spell in some way (damage, for example)
-Can only have 1 of these modifying spells prepared at a time
-"Create Spell" lets you take a spell you've modified using "Modify Spell" and save it as a permanent new spell
-Trying to lean more into the flavor of what wizards are, their ability to "hack magic", and emphasize planning possibilities
-Evocation:
-Now actually gives evocation spells (others will have the same)
-Potent Cantrip now works with attack cantrips as well
-That's about it
-Weapon Mastery is huge for fighter and barb, entire new subsystem
Fighter:
-Second Wind more than once per rest, number of uses increases with level
-Features that let you customize Weapon Mastery properties
-Unconquerable - Extra use of Indomitable, with Second Wind at the same time
-"Big ticket" is the weapon mastery system and relating fighter-specific features
Champion:
-Intentionally most simple subclass, beginner friendly
-Still has improved crit
-Remarkable Athlete was low-rated, replaced with 2 features
-Adaptable Victor - Change skill proficiencies
-Heroic Warrior - In-combat advantage if they don't have it
-Survivor feature improved, now advantage on death saving throw, and death save rolling 18+ acts as a 20 on the die
Barbarian:
-Weapon Mastery at level 1
-QOL stuff
-Rage persists by just spending a Bonus Action rather than needing attack/damage, but also still persists by making attacks, rolling saving throws
-Rage lasts longer, up to 10 minutes
-Danger Sense and Feral Instinct combined into single feature
-Brutal Critical moved to higher level, but more powerful, scales with your level
Berserker:
-Completely redesigned Frenzy, does not cause exhaustion, instead works with Reckless Attack and causes bonus damage (number of D6 equal to rage damage) on the first target hit when using it
General additional thoughts:
-Tweaked spells and feats in the UA
-New epic boons, get more and more epic with each UA
-This has all just been PHB UA, DMG and MM testing to come