@Areas:
The Fallen Temple (first area) layout slightly changed so you find the quest before the Barracks 
The Servant Dormitory made slightly smaller and changed generation layout a bit
The Upper Temple Halls now has more varied rooms and a rounder feel to it
The Upper Temple Halls waypoint now spawn near the entrance
The Lower Temple Halls is now smaller and leads to the new area: Temple Hallways
Increased chance of Champions and Elite spawning in most small and/or optional areas
Changed layout of the Champions Domain challenge area
@The following areas have been added to the first chapter:
Temple Hallways
Offering Chamber
Hall of Learning
The Lyceum
Chamber of Meditation
Chamber of Healing
@Bosses:
Slightly changed intros of bosses in Act 1 and added closing doors rather than making walls appear to lock you in
Added a new boss to the main story of the game in Act 1 - Mundus the Fetid
Captain Moore is a little faster now
Bosses now drop crystals
Bosses no longer have elemental weaknesses or resistances for a more fair challenge for all types of builds (previously Fire-based builds had a big advantage in many cases)
@Quests: 
Act 1 quest flow updated somewhat
Act 1 quest descriptions and names updated
Added three new optional quests
@Difficulty:
Bosses now have much higher chances of high quality loot on Heroic and Legendary, and slightly lower on Normal and Casual
Higher difficulty now adds even more magic find
Increased amount of Elite packs spawned on Heroic and Legendary
@Skills:
Increased the boundary of which skills are removed from screen - they can now be active just off screen for a while before disappearing (previously they'd disappear upon touching the edge of the screen)
@Berserker:
@Lightning Jabs and Blazing Fists:
Updated visuals
@Fists of Fury:
Now attacks with double attack speed, but for less damage (max 100% [technically 200% because double attack speed], down from max 170%)
@Templar:
@Sear, Smite, and Sparkstrike:
Updated visuals
@Holy Hammer:
Updated sound and visuals
@Divine Blade:
Now lands at cursor
@Blessing:
Updated description, now heals 47/54/61/68/75% of damage (up from 10/15/20/25/30%) to make it more worthwhile
@Holy Fire:
Now properly lights up
@Starfall:
Reduced maximum damage to 250% (down from 400%)
@Warden:
@Chain Lightning:
Now hits more targets on an earlier skill level, but same at max
@Warlock: 
@Warp:
Improved visuals a bit
@Hellfire:
Damage nerfed, now deals 100% + 4% per rank (down from 120% + 5% per rank)
Amount of fireballs reduced to 10 (down from 14)
Description updated to show how many fireballs are created
@Items:
Epics are no longer called epics, as it was pointed out that they aren't very epic! They are now called "rare" instead and as such, the drop rate is slightly lower, for balancing
Most accessories that had special texts on tham have been upgraded to Unique quality, some old Uniques have been made Legendary with improvements
Ring of the Three Suns now always roll fire damage
Molten Orb now rolls slightly less fire damage (but still more than a random item may)
Light's Blessing now increases all damage by 10% for 5 seconds
Skyshard now strikes thunder on all enemies around you
Smoldering Gemstone now releases a nova of Firebombs!
@Added new accessories:
Ring, Loop, Iron Band, and Circlet - random rings that may drop with fully randomized stats of Enchanted quality or higher
Amulet, Necklace, and Medallion - random necklaces that may drop with fully randomized stats of Enchanted quality or higher
@Added the following Unique and Legendary accessories:
Frostband - Unique, Frost damage
Static Loop - Unique, Lightning damage
Miasmic Band - Unique, Poison damage
Enforcer's Ring - Unique, Physical damage
Righteous Circlet - Unique, Holy damage
Blasphemy - Unique, Shadow damage
Hoarfrost - Legendary, Frost damage
Ring of Thunder - Legendary, Lightning damage
Gaia's Binding - Legendary, Poison damage
Kingsrock - Legendary, Physical damage
Divine Link - Legendary, Holy damage
Death's Bond - Legendary, Shadow damage
Note: there are already existing ones for Fire damage
@Sets:
@Firelord's Regaila:
4 set bonus now instead increases the duration of Infernal Demon by 100%
@Corruptor's Plague:
4 set bonus now makes Pool of Corruption cast Poison Skulls randomly while it lasts
@Monsters:
Changed how monster spawns work, you will see some changes in monster pack sizes and special monster health levels
Increased health levels of Elites and Champions, but reduced the effectiveness of affixes like "super health"
Champions names are now in gold colour, as the orange was hard to read over the healthbars, and Unique monsters have green names
The champions of Champions Domain have new skills!
Added some new variations of monsters to the new areas in Act 1
Experience values of tougher monsters have been increased
Explosive monsters now deal a percentage of their maximum health (instead of maximum damage) upon exploding. The damage is reduced the further away you are from them
Wraiths now cast blood bolts instead of the purple magic projectile
Evasive monsters are now less... evasive, making it less painful for the melee characters in Act 2
Ranged warping monsters are less likely to warp and have a longer cooldown on the warp. Melee enemies are the oposite
Elven rangers of all kinds are moving a little slower
Some unique monsters now have light around them
Reduced damage of Spellbinders
Reduced damage of all types of Stags
@Sounds:
Some new sound effects for some monster and player skills
Added sounds to the skill trees, one for spending a point and one for reaching max rank, as well as swapping tree
@Achievements:
Added new achievement to beat Mundus
Added new achievement to complete quest "Vault Hunter"
Updated icon of "Restless Sleep" achievement
@Quality of life:
Movement should feel a bit more responsive now (faster acceleration)
You can now use the left analog stick on gamepads to navigate menus, the inventory, etc
Waypoints now automatically activate when you get close to them
Opened chests and used shrines no longer light up when you hover the cursor over them
Gambling and getting an Unique or better item now plays the Unique/Legendary drop sound
The Deepwood Shrine should now have a floating exclamation ("!") mark on it whenever you have acquired all keys
Reduced experience needed from levels 1 to 5 by a lot, so you get to the next skill tier faster
New characters start at level 0 now and are levelled up to 1 when first played, to emphasize on the first skill point being available
Added option to reset progress of a character, deleting obtained waypoints and all quest progress, so you can play fresh with an existing character
@Misc:
Added stat tracking for amount of Elite (blue name) monsters killed
Added stat tracking for amount of items dropped overall (this one was actually tracked per-character but wasn't visible until now)
Sgt. Jorgen now drops you a key for his chest
Increased price of gambling a little
You can no longer push enemies by walking into them, instead you slowly walk past them
Updated class info texts when making a new character
@Interface:
Announcements / on screen promts are now drawn higher on the screen to be less obstructing
The number of zombies left to kill for the quest "Trapped Refugees" are now displayed on screen when killing one
Improved text readability of some menu options
Player level is now displayed on the HUD
Added an option to the gameplay menu to automatically inspect stuff that the mouse hovers
The "Normal" difficulty is now highlighted and displays info when going to the difficulty screen, instead of casual
@Fixes:
Fixed tabbing out of the game causing the mouse to stop working in-game
Fixed inventory instantly closing when binding it to open on gamepad (B) button (as B is cancel button by default)
Fixed gamepads being a little unresponsive in the interface/inventory while playing multiplayer
Fixed crash on levelling up during a boss fight 
Fixed cave entry and exit being difficult to click
Fixed the High Priest having too wide collision box, getting him stuck on corners
Fixed issue with gambling where the item is rolled whether or not you have space for it
Fixed magic find achievement triggering from difficulty bonuses
Fixed Ragnarok Guard granting 500% attack speed
Fixed Firelord's Amulet not having an icon sometimes
Fixed gambling a legendary item not adding to legendary items found statistic
Fixed dropping legendary items from inventory counting towards legendary items found stat
Fixed experience on that stat screen being displayed incorrectly
Fixed typo in Barkskin passive skill
Fixed typo in general quest reward description
Fixed companions being instantly resummoned when gaining a buff from for example your base skill
Fixed the coin icon being shifted to the right
Fixed minimap icons disappearing when you left the zone
Fixed stat achivements not being triggered by shadow damage and shadow resistance
Fixed accessory "Light's Blessing" special effect
Fixed stash not saving if items had been moved
Fixed possibilty to withdraw item stacks from stash into nearly full stacks to make stacks beyond the limit
Fixed being locked out of the boss fight in The Stampede if etnering form the north
Fixed Light's Blessing proc being overridden and deleted by pretty much everything
Fixed the shared stash not being refreshed for all players on screen if several managing it at the same time
Fixed monster spell "screaming skull" just going in a straight line where it was supposed to circle them
Fixed some magic projectiles sticking to walls like arrows instead of disappearing
Fixed stashing items bound to belt allowing to bind for example equipment to belt 
Fixed error in generating the Upper Temple Halls which causes unreachable areas
Fixed problem with movement stopping seemingly randomly (was related to picking up items / certain keystrokes clearing keyboard input - very common in multiplayer)
Fixed issue where some ranged enemies would lose their ranged status if the player left and then returned to the zone
Fixed unique item "Qu'ayles Wisdom" not rolling any enchants
Fixed Elite and Champion monsters sometimes getting duplicate affixes
Fixed skills that only had points from item/set unbinding when entering a new zone
Fixed Cael'is not playing all his sound effects (hurt groans)
Fixed Cael'is explosive arrows creating a single floating arrow after exploding
Fixed sale price of stacked items listing as 0 when selling an item from a stack
Fixed rare crash on Oakstorm the Archdruid fight