Age of Empires II: The Age of Kings

The Good
The amount of options you have in this game are incredible. The included mission packs are insanely fun to play, including such famous people as William Wallace and Genghis Khan. There is a lot of game to play, and barely any micro-management is required to keep your cities up and running and to keep on producing units.

An included mission editor makes the game even greater, as any kind of mission you would like to create can be made with an easily learned scripting system.

The Bad
The pathfinding of the units is not perfect, but no pathfinding is perfect, and it is generally better than other games from it's time period.

The Bottom Line
The greatest RTS ever made, with limitless amounts of options for all players, and with the included mission editor, even more options as you can download other peoples works.