Quality of Life

The following quality of life changes have been made in Path of Diablo.

General

Trade website with excellent functionality
No cheats, bots, maphacks, multiclients, and third party programs (check the official FAQ for details)
Dozens of stable regional servers (many paid for by the community)
Character account limit increased to 18
Global chat functionality
Seasonal ladder achievements
Players can now see games at lower difficulty levels in the lobby (not just the current difficulty)
NOTE: This is a very friendly server quite different than Bnet. Try to look out your fellow adventurers (you will very often find others do so). Players can be banned for griefing or otherwise egregious play.

Advanced character sheet with many new stats visible (hit "8" by default)
Automatic party formation when entering new games
Game timer
Shrines can be active simultaneously (and no longer overridden by curses)
'Move Only' command to prevent deaths due to unintentional monster targeting
Renaming of several affixes, items, and skills, and rephrasing of various skill descriptions to increase clarity

Loot filters that are fully customizable
Inventory size doubled (but charms only 'active' in the lower half to prevent balance issues)
Stash size increased (from 6x8 to 10x10)
Inspect the gear of allies
Perming games now only requires 30 seconds
Quickly move items to stash or ground via control/shift right click

Item drops fixed to /players 8 (does not affect monster hit points)
Runes drops occur at a much a more linear rate at higher tiers
Characters start with +100 stamina and base mana regeneration increased by +100%
Slaughtering the Cow King no longer prevents creation of the Cow Level in future games
Changes to a handful of monsters (e.g. dolls, gloams) to limit very specific instances of previously unfair deaths in Hardcore mode

New build-defining skills, reworked legacy skills, balance changes, and more
Unique Item reworks and other changes
Runeword and Set Item changes (e.g. Enigma's teleport)
New crafting system to help unique items compete with high tier runewords
Melee Splash jewel added to help physical builds compete with elemental casters
Mercenaries from all acts are now viable