It is VERY good. One of the best mods for Dominions I remember ever seeing. The graphics are very good, and fit very well with the other troops. The units are well balanced, but perhaps a tad expensive - Peasant Spearmen/Swordsmen could be just 8 gp and both Footmen just 11 gp, IMO. National troops are usually a bit better than the independents.
Blue Wizards lack waterbreathing. That contradicts their description a bit.
Does "the sense of justice" of the Red Wizards do anything? Patrol bonus, #okleader, anything would do, really. Lightning Resistance isn't a good ability either, IMHO.
You might want to add a "Grey Acolyte", a mage with one 100% elemental random, recruitable in all castles but costing almost as much as a full-trained Wizard from the capital, 80 gp or so. Of course, if you want to make mages rare and national commanders common on purpose, feel free to ignore this.
Halberdiers and Brown Wizards both mention that they are renowned for thier fortitude. I suggest giving both just encumberance 2. Also, Halberdiers have defence 13, Foot Knights just defence 11.
All of their heroes are WONDERFUL! I also like how you used so many of the new modding capabilities in Dom3 in simple but effective ways. The heroes, again, but also the new magic sites. Ley Line Conflux... I love it!
EDIT:
Also, forgot two things:
The national pretender is very interesting. Perhaps he should have defense 5 instead of 0, too. Also, he seems to be missing his weapon (Spear). It might be impossible to actually give him attacks, what with the #immobile tag. You might want to change that to mapmove 0 instead, if that's possible. I like the idea of a pretender who has limited ability to move, but won't leave the capital.
High King could have a magical scabbard giving him rejuvenation. That'd also increase his maxage a bit, so he'd be less likely to get afflictions (even if he was old).