I have every Age game ever made, including Age of Mythology and the expansion - which you haven't mentioned :P
Age 3 is, to put it simply, a good game. It's got as many new good ideas as all the previous age games had back in their day.
At the moment its still full of techincal bugs, and if you're planning to play online, you won't have much luck.
The campaign, of which I've played about 30% until now, is pretty good. Not exceptional, but has good a good plot and the voice acting isn't as bad as in some games.
For skirmish games, there are some things missing... first, its like AoM, you can't choose your map size. It's auto-sized for the number of players. Second, the only type of skirmish game is Supremacy. For some reason, there's no Deathmatch, theres no King of the Hill, wonder race, or anything else... There are, however, random map scripts and scenarios for download on the official community site
www.agecommunity.com
Multiplayer is really where it's at though. Find yourself a couple of friends and make a LAN or play by Direct IP. The game's fun value really comes to the front line in multiplayer!