AOE2 is simply amazing...I've never played AOE1 so I can't make any comparisons, but look--AOE2 beats out much of the great RTS games (including my favorite game Starcraft) by including 13 civilizations with  infantry, cavalry, archery, naval units, siege weapons... and all kinds of  defense measures, including all-mighty castles and bombard towers.  The  diversity of units might be less than some widely popular games, but you  can understand and feel every single part of this game.  Upgrades from  Cavaliers to Paladins and Archers to Crossbowmen make sense--they aren't  just words from nowhere.  And if you're looking for a great campaign game,  this is it--there are carefully made videos and sounds (just as starcraft)  for the campaigns, and I especially enjoy the diversity of these one player  missions.  The 1st Mongolian mission was very interesting, requiring you to  befriend the different  tribes by bringing them sheep, killing the wolf  pack, founding the sacred relic, etc.  I also liked how this game handled  commerce.  There are a variety of types of resources (gold, stone, food,  and wood to be precise) and you can build trading carts to earn gold by  trading with other players, pay tribute, etc. etc.  This game is simply a  must-buy...it's worth every penny.