If you liked the first, well now you can have it with less bugs, and a nice tutorial, which is quite nice of them. (apparently)

Ensemble Studios has issued an updated playable demo for Age of Empires III, bringing this sample of their new historical 3D real-time strategy sequel to version 1.1. This hefty download has ballooned by another 61 MB, adding "lots of bug fixes, a new minimized UI and a tutorial mode," and as before it contains two single-player campaign missions and a pair of skirmish maps.

Grab it from 3d Gamers