I own AOW3 and its first expansion, Golden realms. I've had a lot of fun with them (200+ hours on Steam). The campaigns are good but I've probably spent more time playing random maps. IMO the game has a lot of replayability because of all the different race/class/magic specialization combos.
Compared to Civ 5 there's a much bigger focus on combat (IMO) and on finding a good mix of units that can support each other. There are some *really* devious unit combinations, and the fact that you get to customize your heros (and even equip them!) means that there's always plenty of stuff to min/max. If you're into that so
I still have not tried multiplayer... kindof afraid to after reading on the forums about the crazy tricks those guys have figured out already
Finally... the map artwork is beautiful!
EDIT: I think a big reason I enjoy AOW3 is that the game promotes being active on the map. The treasure site mechanic means there's always stuff for your units to do (in addition to scouting), even in the first few turns of the game. Half the strategy is squeezing every last drop of usefulness from your troops. For example, if you can fight battle X a little more efficiently then maybe you can attack another site in the same turn, earning additional resources.This comment was edited on Apr 15, 2015, 18:10.