A fine idea Jet. I also wanted to solicit a few more thoughts from you re:Units, since I thought your brief comments were quite on the mark.
* Horse Archers - I think they were nearly absent from Western Europe. The skills were not developed. I would restrict Horse Archers to eastern barbs, eastern civs, and Cordoba. And give them a bonus against melee units.
* in general the units felt like they should be streamlined. Too many units that are too similar to each other, with rock-scissor-paper bonuses that are too small, and unit classes that aren't clearly distinct in a satisfying game design way.
* Mounted Infantry, Foot Knight - Something about these units doesn't quite feel right. The Mounted Infantry feels like it doesn't account for the expense of maintaining horses, and it makes you wonder why you can't add horses to other infantry units.
* I'm not sure but just looking at it on paper, you might need to make the later units stronger. Time-restricted mods often have the problem that late units are not sufficiently stronger than early units. The choice between research and production ends up not being balanced. It ends up that you only need to research some intermediate unit and spam it.
I agree that Horse Archers are a bit awkward as they are -- there will be changes in this regard. Mounted Infantry are also an odd unit. Thanks to that description of why they are odd I will definitely re-examine their role.
Points 2 & 4 are probably related. It was important to us to have relatively small gradations between units, rather than dramatic jumps. This, we felt, reflected the historical period of our mod, where the development of military technologies really didn't obsolete pre-existing ones (things change a bit with the introduction of gunpowder, but we have a lot less tests from late game for obvious reasons). Your point is well taken though -- research needs to remain important.
I feel that medieval warfare in base Civ is not that exciting, which is why I tried to mix things up a bit. The broadest paper-rock-scissors design (at least in my head) is:
Horse > Infantry > Polearms > Horse
With the added twist that unit costs go like:
Horse > Infantry > Polearm
So that polearms are at least the
cost-effective counter to horse. The nature of combat in Civ (1. Strongest defender fights and 2. City attack is so important) makes hard-counters very tricky to get right in my opinion. But it is very satisfying in-game to have predicted the enemy attack units and built the right response.
There's basically another layer of rps tucked away, which is:
Armor Piercing > Armored > Non-armored > Armor Piercing
where any unit could be Horse or Infantry (although a lot of the Armor Piercing units are archers). Interleaving these two trees effectively is difficult to get right.
Do you have any further thoughts? Would you care to try re-plotting a portion of the unit tree (at least on paper)?