AOE II is a great old school game. Now that I have AOE III, I only occasionally play AOE II, but when I do, I'm hooked on it for a week.
AOE II has great graphics, great plots, and a really good range of possible units and civilizations. You can play as everybody from the Saracens to the Celts. They have Cataphracts and Woad Raiders. Trebuchets to battering rams, and champion swordsmen to paladins.
Great game, I recommend it.