Monstrous mortal empires map -> has everything game 1 has + most of game 2 + a lot of new provinces.No regional ocupation -> better variety in the campaign map although each faction gets penalties in some climates.Lots of new matched animations -> expect LL and monsters to now have unique animations.better lighting -> the new lightning system allows for spells and light effects to have much more 'realistic' effect in battle.Doubling down in making each faction play differently -> new races have more unique mechanics as well as updates for game 1 races.More types of battles -> island battles (no autoresolve at sea!), choke-points, Gates ,etc.
Click to shrink.I'm going to be shortening a lot of stuff to give you an idea of what wh2 improves over wh1.
