Bamflux,
As you know I have been running your civs alongside the other popular fantasy CIVs to see how they balanced against them, how they interacted and if there were problems when bringing them all together. In this they have been added into scenarios with the Faerun Civs and the Skyrim Civs - as both are available outside their total conversions and are the two most prominant and available groups.
All in all your CIVs match up quite well with and against these two groups (I run 20 civs and 20 CS, Huge map, Emperor and with a LONG list of enhancement Mods in each game and finally an Era Block at the Renaissance period, to keep everything medieval/fantasy era).
I cannot see anything that creates an OP situtation (or under-powered as far as that goes) so far, and other than asking you to consider a two-tiered approach to the UU - one lower and one upper tech level unit - they work together flawlessly. What I mean by this is perhaps having a uniquely named early unit, that can be upgraded into the UU once that tech is acquired to allow time to gain some early promotions that will carry over once the UU is gained.
In a couple of cases, the UU becomes obsolete, comes too late to gain much Experience (promotions) or is technologically replaced too soon after you can start building them and you get little time to field and promote them. I think a 2-tiered approach could provide a longer lifespan of these special units, especially if you can level them up before upgrading. This is true for some of the other CIVs and not just yours, and something that I think you can address if you want to and allow the players to spend a little more time with these really nice units before they are phased out by tech advancement. The one that immediately comes to mind is the 7th Legion Cavalry that goes obsolete at Knight and not cavalry, so you do not have much of a chance to buy/build before it goes away. If it was replaced at Cavalry, you would have time to build, get a promotion and then upgrade/replace it. OR.. the 7th Unit Cavalry would not go obsolete; instead give it a healthy promotion when the Cavalry Tech is achieved and even a smaller promotion as it passes the Knight Tech, these would allow you to develop and utilize the unique piece(s) over the course of several eras.
Some CIVs have starting advantages, some mid-game and a couple late game perks, but over the course of 250+ turns they all mesh together very, very well. no glitches, no problems even under the heavy Mod load I put them under. I noted to you the only one that seemed slower to expand than the others, so I will not add that here as you may have already addressed it.
I do have a question for you - is it at all possible to flavor the Civs so that those that are inheritantly "evil" will stop starting out Friendly to the Civs that "should" be their natural enemies. It gets disturbing when the Civs that you would expect to ally with you start out as neutral, and those that you would think would be opposed to you begin as friendly. This is not just your Civs, but true in most regards of those that I included. It would make the scenarios a little more realistic to expectations.
For example, why is the Lich Lord so bloody friendly to everyone? I expect him to be the all-out, absolute antangonist and other then his constant political friendship requests, he is not antagonistic, annoying yes, but threatening not so much. This might be just how "I" perceive the CIV, but it feels odd to have him trying to be everyone's friend. NOW... once you attack him, he is a great foe, and that CIV's unique traits play out very well, it is just during the non-combat phases he seems overly "nice".
Given all of that, my only other comment would be to consider increasing the Orc's aggression even further. Yes, they reacted very well once they are dragged into war, but they are not as aggressive as say Ghengis Khan's units, which I would expect them to compare with, in their representing what I had thought was a much mjore warlike (aggressive) CIV. Of course, you may not have wanted them that aggressive, and that may just be a differance between WOW orcs and the ones I am used to, but I'll suggest it anyways, just in case you may consider it.
Fantastic work so far, I have seriously enjoyed everything you have done so far and I cannot wait to see what you do with the Tech Tree.