I just wanted to address some things that I haven't read here. I think all the unit models for Dale and Gondor look amazing so if you keep it like that I am fine with that.
1) When I played city assaults I wasn't able to place units onto them properly. Always looked a bit buggy.
2) Sometimes the texts in the battle loadingscreens are too long and are cut off. For example the book scene when Sarum tries to convert Gandalf to the "evil side".
2.5) Not sure if you can change that, but your custom texts are sometimes very long and I hadn't finished reading when it swapped to the next text.
I hadn't a lot of time to play RoM yet, but now the school year is over I will play it every day and come up with some more feedback soon.
Correction: 1) When I played city assaults I wasn't able to place units onto barricades properly. Always looked a bit buggy. (But maybe you won't use barricades in your custom battles, if thats the case this comment is useless anyway.