Europa Universalis III: Heir to the Throne brings in new cool features like:
– Brand new Casus Belli system, where wars have specific goals from start to finish.
– Monarchs now belong to dynasties, with new influence on the diplomatic model.
– Increased Holy Roman Empire and Papacy options for more powerful ruling
– New diplomatic options for Merchant Republics
– Enhanced “Cultural Tradition” and recruitment of specific advisor types
Please have in mind that Europa Universalis III: Heir to the Throne is just an expansion and it requires the original EUIII game, as well as the previous two expansions to work. If you don’t have them, you could get a really cool deal for Europa Universalis III Complete over at Amazon.com! Have fun!