A great addition to a great series
Medieval 2 total war doesn't dissapoint. Set in the medieval age of knights and castles, Medieval 2 total war lets players assume the position of one of the major nations of the period. Religion plays an important part, as it affects the happiness of settlements, relations between factions, and most importantly for catholic factions, relations to the pope.
The pope is an unplayable faction with one city, Rome. Though obviously not a threat militarily, the pope issues missions, calls for crusades, and runs the inquisition.
Economy is a big part of the campaign. It fuels armies, serves as bargaining chips in diplomacy, and well, money is always important. The campaign map is made up of cities and castles.
Castles serve as your main producers of advanced military troops. You can build buildings such as stables and barracks to train better quality troops. Also, castles grow over time (this is increased by farms and such), once upgrade they provide better defence, and a larger variety of troops and buildings.
Cities are the main economic centers of your empire. They are hubs of trade, and a good place to tax. Various buildings increase trade, thus increasing the amount of money flowing into your coffers. Cities also train troops, but not as large a variety as castles.
Economy and Religion are all important, but lets not forget the WAR. The battles are still as epic as it's predecessors. The scale allows for thousands of troops to be on the field at once. Allowing a truly large scale epic feel. Sea battles are unfortunately only auto-resolved.
War can cause bad feelings between nations. Such as attacking someone's ally. Catholic nations also have a larger burden. The pope will not be happy with you for attacking other catholic nations, though attacking islamic, pagan, and heretical nations gains favor. If you do not heed the word of the pope, it will affect your diplomacy and the happiness of your nation.
So overall:
THE GOOD
Epic battles
Scale is immense
Good Campaign map
Good number and range of units
Ok number of nations
Don't need a monster of a computer
THE BAD
Hard Drive Hog
Auto Sea Battles