I dived into your mod and I really like it. It shows that you tried to balance a lot of things with minute attention to details, I really appreciate that. I also appreciate that some monsters or abilities are powerful, but you did not go the easy way of adding pack of 9 dragons and suchlike. Subtlety and elegance would be a good description of your mod.
Lore also is really well written, again with attention to details. Also great is that you even added icons that are only there to warn and help players. Last point, races are very diverse. Kudos!
I played the Gnomes, and died from a lizardman invasion on turn 89, must be because I set them at ridiculous level 
Some remarks if you allow, mostly on gnomes.
They have a spearman design with crystal, is not dangerous for the AI (preventing it to build them if no crystal around?)
All city battles show a forest of dead trees, but not buildings in gnome towns. Cosmetic? Not only, because in my last big battle where I make a last stand with 11 total units, my sovereign was stuck in a tree and could not move out of it.
My initial hero was the Gnomish hero that was dishonored. -1 prestige is really tough at start... perhaps -0.5 would be enough. That or at level 5 his ability disappears if this is possible (he stopped at level 4)
Two suggestions that you may find thematic to the Gnomes perhaps:
Perhaps they can have normal move cost in hills.
I would love to have them get a 1% return on interest on gold stockpiled, that would be so Gnomish while not that powerful.
I also encountered the Dead Legion. They are demons if I get it right. So questions...
1. Why they color is bright yellow and not something red or purple, whatever?
2. They have a unit template named spear maiden... Not quite in theme I would say. Perhaps you did not had time to propose custom units per race, but I think that would be a major feature that would give much flavor to your mod.
Thanks for your hard work. I'll restart a game with a more moderate setting now, perhaps AI expert will be enough.
edit, in raceconfig_deathlegion.xml you have
<PopulaceName>Frost Giants</PopulaceName>
I'll also probably replace their ZOC color by their UnitClothing1Color which seems much more appropriate.
