The Age of Kings made perfect.
Notable among the additions are American civilisations. Lacking in mounted troops, these cultures will have to rely on their strong and fast infantry, making for an interesting change to the generic strategy of the other nations, where cavalry always plays an important role. You will be able to test the viability of infantry-only armies in one of the four new campaigns - Montezuma's defense against the Spanish invaders. As in the base game, the campaigns are interestingly scripted and woven around captivating storylines. Besides Montezuma, you will follow the trials of El Cid and Attila then play reenactions of the world's greatest battles of the period including Agincourt and Lepanto.
Although hard to believe, the interface and the AI of the base game was improved upon in The Conquerors. The behaviour of your units is full of helpful bits, peasants building structures will help with other work once their task is complete, or if building a resources gathering structure, will start gathering resources themselves. There are many other nice tweaks really helping with the micromanagement, for example, there is a farm queue, allowing for auto regrowing for farms. Infantry can now garrison battering rams, making them faster and stronger in addition to the infantry being safe from enemy archers and ready to protect the ram from infantry should enemy units get close. This makes rams suddenly quite useful and, if well deployed, deadly units. As another welcome addition, naval forces can be grouped into formations the same way ground forces can.
Bottom line: The Conquerors corrects almost all the slight problems of The Age of Kings, adding four new campaigns of high quality for hours of historical strategic enjoyment. A must have for all Age of Empires fans.