Legendary, amazing, and will never get old.
I have played this game since when I was about 6-8 (so around 2002-2004), and still enjoy it today. The replayability level is very very high.
The graphics are amazing for its time, and still look very nice and nostalgic today. The music is also kinda nice.
The only slight issue though is that if you have Windows Vista (and maybe 7 too), you might have some issues with the coloring. The only ways to fix it are to either pause, Ctrl+Esc, and go back to the game; or try to change the resolution to 800x600, and back.
You can play the Campaign, which follow leaders such as Genghis Khan, William Wallace, and Joan of D'Arc.
There is also a mode where you can set up a match against the computer (which in my opinion, is the best mode). There are a few match types you can choose from, such as Random Map, Deathmatch, and Regicide. Each civilization that you can choose from is unique in its own way, starting from the architecture, down to the small details such as the soldiers' and villagers' ability to speak in their native language.
The interface is simple and clean.
You can also create your own map, but if you want to make a good one, it'll take some time and patience.
There's an ability to play online and over LAN. I haven't tried the online mode, but LAN seems to work fine.
I probably haven't mentioned every feature in this game, but you can read the GameSpot review for that.
This is one of the best, if not the best RTS game ever created. If you wasted your time reading this review, you should waste no more time and buy this game. Even if you're not a huge fan of RTS games, you should get Age Of Empires II anyways. It'll MAKE you a huge fan.
Just my 2 cents.
Buy this game.
Have a nice day.