If you look at it from a general real-time strategy(not the city-building type) point of view, Age of Empires: The Age of Kings is the king! It was lots of fun to play, and to see at that time. Even now, after it’s successor (Age of Empires 3) launched about a year back, there are people playing Age of Empires: The Age of Kings. The reason- it’s a classic!
Age of Empires: The Age of Kings is a basic resource-gathering and army-building RTS, which is set in the medieval times. One of the highlights of the game is the campaign mode, which is in the form of the narration of a story, of great kings and warriors i.e. the persons you’ll be playing as. This concept was unique at the time, and it was quite cool.
The battles in Age of Empires 2, were great, and the game itself was quite deep, with a lot of technological and military advances in it, without forsaking on fun, and keeping it quite simple and straightforward. Resources had to be gathered for building up your armies and constructing wonders, and they were of four types: Wood, Stone, Gold, and Food. There were A LOT of playable factions and they were quite unique in their own way, although based on the same structure of units.
To sum up, the graphics in Age of Empires 2 were great, the sound and music were great and the online play was great. A great game to play!