The grandaddy of the RTS genre and still the best. A 2010 review looking back..
Age of Empires II gameplay followed the traditional economy, population, and military balances. The player chooses one of thirteen available civilizations to manage and bring to glory. The civilization starts from humble beginnings and slowly becomes a powerful nation... or a dead one if you make mistakes. First the player must quickly build his economy by gathering natural resources while building his population in order to maintain his or her army. A very simple idea to pick up, but a very challenging game to master. The single player campaign makes it worth the admission as the player gets a history lesson playing alongside famous heroes of the past such as William Wallace and Joan of Arc.
What really creates replay value is the online multiplayer that is still active as of June of 2010. The game offers traditional gametypes such as Deathmatch, Team Deathmatch, and other typical RTS games, but the various online modes created by custom maps create a new experience. Age of Empires II set the benchmark for other games such as Warcraft 3 to follow, where custom games such as the ever popular Defense of the Ancients were created.
The graphics were great.. back in 1999. For 2010, the graphics are terrible but they do not detract from the gameplay. However, if you run Windows 7 you might have a bit of trouble getting the game not to crash or the colors to work perfectly. If you run Vista, you might be out of luck.
Overall, this game is the best game in its series, and it could very well still be the best game in its genre.