Alpha Centauri wasn't quite the commercial success that Firaxis hoped for, but it did earn a loyal following. These fans looked past Alpha Centauri's similarity to Civilization II and reveled in its deep turn-based gameplay and strong premise: an interplanetary war for military, economic, cultural, and scientific dominance. But many others shied away from Alpha Centauri because both its alien factions and its technology were too unintuitive. Fortunately, Alpha Centauri's official expansion pack, Alien Crossfire, resolves at least one of those concerns.
As with its predecessor, Alien Crossfire has a good background story, which is unusual for turn-based strategy games. The planet Alpha Centauri was apparently seeded with great power by an ancient alien race. Now, the descendants of those aliens have returned to claim that power. However, the aliens are divided. Their two factions, the Caretakers and Usurpers, have opposing views on how to exploit the planet. In addition, they are joined by five new human factions, including the cyborgs, the pirates, the data spies, an ecological cult, and a drone proletariat faction. Although there are many to choose from, it is now much easier to decide which faction you want to play because you can see all pertinent information for each new faction from the selection screen.
Each new faction has different specialties. For example, the Cybernetic Consciousness gets better research because they have computer-swift brains, but they have stunted growth because replacing their minds with cold computers weakened their ability to interact with others. The Nautilus Pirates get free shipyards and several early sea bonuses, although they also suffer in growth because their swashbuckler culture shuns family life. The alien factions are particularly potent, for they begin play with a strong alien military unit and also possess scans of the planet's surface. These alien factions share some bonuses but also have a few unique advantages and disadvantages.
Alien Crossfire's story hints at the possible devastation of Alpha Centauri if the Usurpers can unleash its power. Throughout the game, fictional book chapters will detail the first meeting of aliens and humans, the unsavory means by which the Usurpers studied their human captives, and the thrill of victory after the Usurper or the Caretaker defeats its hated rival. Because the mind-sets of aliens and humans are so different, you won't be able to communicate with the other race until you research the right psyche technology. It's a nice touch that you actually have to study your alien counterparts before you can even speak to them. However, there are sometimes a few discrepancies in the progression of the story. As the Usurpers, you might eliminate the Caretakers early on, but subsequent entries in the book will keep referring to how you need to befriend or enslave the humans to defeat the already-defeated Caretakers. In addition to adding new factions, Alien Crossfire also introduces several new technologies, new units, new graphics for analogous alien units, and even some new secret research projects. Unfortunately, all the new technologies are as unintuitive as the original ones, although Alpha Centaui fans familiar with this sort of technobabble probably won't mind it the second time around.
Usually, expansion packs for such games simply add new scenarios (as with the Civilization II packs) without really expanding the gameplay, but Alien Crossfire adds a great deal to the original game. While Alien Crossfire's core game is still very much the same as its predecessor's, the new factions, technologies, and projects increase that core game's depth. These additions don't make the game fundamentally different - you'll still feel like you're playing the same game, even as the alien factions - but you'll recognize that you have a few more options to explore. The additional victory conditions also heighten the experience because they at least superficially highlight the differences between the humans and aliens. Because it makes no drastic changes, players who didn't like Alpha Centauri in the first place will find nothing in Alien Crossfire that will change their minds. However, fans of the original game will want to get the expansion pack for its interesting alien factions and new technologies.