PD2 aims to maintain the Diablo II: Lord of Destruction experience and provide consistent ladder resets while improving on the game as if development never ceased.
Major updates and ladder resets every ~4 months
Increased build diversity & item balance - PD2 has reviewed every single item and skill to give them a purpose to be considered in mid and high-end builds.
New endgame areas (maps/dungeons)
Maps are comparable to vanilla endgame areas, making both new and old areas viable for farming.
Dungeons are extremely difficult group-based maps that offer new challenges and rewards for those interested. Dungeons require teamwork and variety of composition such as supports, tanks, summoners and damage dealers to clear.
PvP Support
Many other improvements - see General Changes for an overview of changes relative to vanilla D2.