Sid Meier's Civilization III

The Good
Many things. First, settlers and workers have no defense or attack. No longer can settlers take down bombers. Strategic resources like iron and uranium add much more strategy to the game. Planes are much better. Now, you just bomb stuff instead of moving them. Instead of having super-short range ICBM's, they are capable of hitting anywhere, just like real life. The controls are as simple as previous ones of the series. More than 2 ways to win the game gives it more replay value. Finally, civ-specific troops and attributes give more variety with civs. Other than the things I listed earlier, the game is mainly a better graphics version of civ 1 and 2.

The Bad
No multiplayer. Small AI glitches also make things annoying. They build cities on your colonies, and enemy troops move back and forth on their borders, like they are patrolling. Also, the combat can be incredibly lame. A horde of horsemen will attack and defeat your tanks. Spearmen can successfully defend against machine gunners. This detracts from the realism the games exudes in other areas.

The Bottom Line
If you are a fan of civ2, than this is the game for you.