Yeah, I bought it and beat the campaign already. It's interesting though a bit questionable on how much strategy you can really use. Most of the campaign sees the computer being a cheating bastard and producing troops at a speed that its resource income should never permit (you'll see it spam really expensive units as fast as the build button recharges) and it tends to turn into a battle of attrition, keep throwing units at the enemy in the hope of slowly making up ground and pushing the enemy back and also hoping the computer won't nuke your advance with a spell or three (which it also casts as fast as they recharge, no mana limit).
The faction balancing is pretty questionable as well, the only Viking unit that can really hurt an Aztec giant is the axe thrower because the giant stuns enemy melee units before they can get an attack off but the Chinese counter giants with almost no effort since their ninja monkeys can just stun the giant to make him easy prey and their zen masters can just instakill the giants with force choke. Meanwhile Aztec mana regenration practically requires sacrificing units which means spells like mind control are nearly pointless since you have to trim your ranks more than you grow them with it while the Chinese only need to grab tower positions to boost their mana which they can then spend to clone their own units, INCREASING their force size (and the effect can be fairly large with a good bit of mana). Plus the Chinese get AOE with their basic ranged unit, while the rocket dude does cost more than other factions' ranged units a mass of rocket dudes is unstoppable without magic. Just kills any number of units. The vikings need the catapult which costs a ton and shoots slowly (also the freeze hammer which just tends to die before getting even one attack off) while the Aztecs only get AOE on the giant which obviously has to get in range first (so they can't apply AOE to massed rocket dudes). Seriously, rocket dudes own, add the ability to clone units on the field and the unparalleled stopping ability of a melee unit with the magic shield (which also prevents stun and knockback so giants can't get past) and you can form a moving wall of death that GROWS as it moves across the battlefield. I guess you should AOE magic nuke them but the Vikings only get AOE on their superweapon spell.
Meh, I'm starting to ramble. Either way, so far the Chinese seem to be the most capable to kill units of any type, mass spam with rocket dudes and single, large units with zen masters. Or, if in doubt, clay warriors plus focussed arrow rain.