The two first games in the Europa Universalis series were all about strategy on a grand scale in a realistic (albeit alternative) historical setting, and this game follows the tracks of its predecessors. In Europa Universalis III (EU3) you take control of any state in the world at any date from 1453 to 1789 and - possibly - guide it to greatness, until the end date, 1792.
EU3 takes everything from Europa Universalis II, puts it in a 3D engine and introduces several new major features, such as being able to change the form of government, national ideas and a military unit system similar to the one found in Victoria. Another aim of the developers was to create a better tutorial and manual, for an easier learning curve.
In EU2, historical flavor was added through the use of historical monarch lists, generals and events. Any important event in history was portrayed with a description and the player was allowed to choose the outcome. In this sequel however, everything starts just like things were at that point in history, but both monarchs and leaders are semi-random, with suitable names for each country. The historical event system was also done away with- instead, the game generates suitable events based on the situation - from revolutions to succession crises.