All new Naval battles
Streamlined formations and pathfinding
Wide variety of unit abilities and fortifications
-Especially Dismounting in battle, which was missing in M2TW
Using Cover and Garrisoning Buildings
Replays for Campaign Battles
Units talk in native language
Overall smarter Battle AI
Campaign and Battle AI communicates (don't really know yet
Streamlined and huge Campaign Map
All new Technology system
Streamlined Recruitment
Streamlined Diplomacy
Streamlined Trade
Streamlined Agents
More field battles vs sieges
Streamlined intercept zone
Name your own units/ships!
No more camping on your neighbor's lands
Queens

Governments, Revolutions and Rebellions/Emerging Factions
Beta for Multiplayer Campaign coming after release