When Microsoft re-released Age Of Empires II as the HD Edition, I can't tell you how excited I was. With widescreen support, updated graphics and interfaces, multiplayer and workshop support, this classic game that I binge-played as a kid just got even better. I've deposited countless hours into this game growing up and played local-multiplayer with my sister every day. In later years we used GameRanger to play multiplayer verses other players, even though it wasn't super ideal.
In my opinion, Age Of Empires is one of the greatest RTS games to date... even though I play very few RTS games, the ones I have played pale in comparison. AOE II has a deep upgrading and leveling system per game and a very large varity of tribes to choose from, each offering their own special units. You can play on a variety of maps and gamemodes, including ones you can create in the map editor. This is where the Steam workship really comes into play, easily being able to download custom maps in minutes.
The map editor itself is something I could talk about for a long time because it is so advanced. I'll keep it short though and say that under it's surface are the options to create detailed and custom campaign scenarios or maps with custom triggers and plenty of props. If you have the time to invest into the map editor, there are no limites to what you can create.
Age Of Empires II holds up really well for being 15 years old, and if you love any kind of RTS game, Age Of Empires II HD without a doubt should be in your collection. The new expansion packs they added is also a must have, adding new features, maps, and units while keeping it true to the origonal game.