The basic gameplay is nothing new to fans of 4X games: build cities, explore the land, research new technologies, make peace or war with other factions. What makes SMAC an outstanding game as opposed to merely a "good" game is the near-perfect play balance that fans of Civilization know and love. Each of the seven factions has unique advantages and disadvantages which offer excellent replayability. For example, if you play as Morgan Industries, your best strategy is to build your cities and avoid war in the early portion of the game until you can buy your way to the top with amassed fortune. In contrast, as the leader of the Spartans, you will want to attack early and often and avoid letting your neighbors build in peace. Although SMAC inherits the very limited diplomacy model from Civilization 2, the strong economic, technology, and combat models more than make up for this weakness-so much so that you can win the game most of the time without caring too much about your diplomatic stance towards other factions.
In addition to dozens of intriguing futuristic technologies you can research, there are also many sci-fi elements that liven up the game considerably. Not only must you deal with other factions, but you must also contend with the mind worms-- one of the planet's most lethal alien life forms. You will also come across parts of the U.N. Unity (which can contain anything from new units and technologies to more mind worms), and encountering strange alien monoliths which can have unexpected effects on your units. SMAC also features an overarching plot, which develops by way of the "Interludes from the Book of Planet" that are woven seamlessly into the game, giving it an excellent fantasy/sci-fi overture reminiscent of Ursula LeGuin stories. SMAC offers many possible conclusions, all of which are directly related to the ideology and goals of your faction, as well as actions you perform throughout the game.
With a strong AI, excellent play balance, virtually limitless replayability, and overall polish, SMAC is a true successor to Civilization 2 that deserves a permanent home on everyone's hard drive. In a welcome change from today's trend of flimsy manuals that are actually 10-page CD inserts, SMAC comes with an excellent 240+ page manual that does justice to the game's complex, yet accessible gameplay. If you love the game, also check out Sid Meier's Alien Crossfire, an official expansion pack reviewed on this site. Three alien thumbs up!