Imperialism was a bit of a surprise. A low-key, visually stylish economic and military conquest game, it didn't have much flash, but it had good gameplay in the Civilization/Railroad Tycoon mold.
Imperialism II sticks close to its roots. The maps and unit graphics are virtually identical to the first, and the fundamental gameplay is very similar. The main change is in the setting. Instead of playing as a robber baron in the age of industry, you play as a conqueror in the age of exploration. Those are two very different milieus for a strategy game, which helps make this feel like a true sequel rather than an expansion pack, but just by a whisker.
Developer Frog City has done some interesting things with the standard explore-and-conquer format, grounding it more firmly in history. It is still a turn-based strategy game with a tactical military element, but the particulars have changed a bit. When you start a new game, the known world is composed of the "Old World." This can be either a historical map of Europe or a random map. The Old World is made up of established neutral nations. To win, you must control one-half of this Old World. You can do that through military aggression or through economic and diplomatic means.
The rest of the map is made up of the blacked-out, unknown "New World," which you must explore and exploit. Forging alliances with native tribes and eventually taking over their land adds nothing to your total victory requirements, however. If you own the entire New World but still only have control over your original nation in the Old World, you won't win. The purpose of the New World is to add to your economic might: Exploitation of New World resources is essential to funding wars and expansion in the Old World. It's an interesting distinction grounded in historical reality. In the time period of the game (1500-1800), the New World's impact on the Old World was mostly one of supplying resources and influence. The true battleground was still Europe.
Other changes to the system reflect the new strategies and economic realities of the period. Since this isn't an industrialized society, there's no need for mills and factories. Instead, goods are used for trade and sustaining your population. The population in turn is needed to process the goods. The most noticeable addition is the constant need to feed your population, which makes agriculture of central importance. Processing raw materials - the core of economic growth - takes a backseat to feeding the populace. This gets a bit tedious, even if it is historically accurate.
The most welcome addition is the ability to direct research. You can now choose which technology to develop next. Technologies improve the abilities of various units (ships move farther, military units are more powerful) or the yield of tile improvements, such as farms and mines. Internal development is still based on using special units to develop tiles to produce resources (food, minerals, etc), but these tiles must now be linked through a network of roads. Transportation allocation has been removed, so the goods now travel automatically. The military element has also undergone some subtle tweaking. Sieges are more common than skirmishes, and you can move units in any order now.. The latter remains an optional and not very interesting part of the game, but it's there for people who want more control over battles.
Imperialism was a good game with a cult following. You either liked it and stayed with it or found its low-key gameplay boring and quickly moved on. Its burnished bronze and sepia look wasn't necessarily what we expect from computer games, but the look was distinct and worked well in the context of the of the game. Imperialism II is a more refined and interesting use of the same system, with an excellent interplay of elements. Expansion is always checked by practical realities, and every alliance and war has a price. A well-balanced game with these elements is hard to create, and Frog City has done an excellent job of it with Imperialism II.