I have just four complains:
1. City with garrisoned units easily falls under attack , those units being destoyed, despite they had enough HPs to repel one or two attacks more. Severe exploit IMO.
2. Artillery is way too weak - it has just 28 strength, while infantry has 70. It is very ineffecitive to weaken city defences with artillery. Even frigates and WWI aircrafts are stronger - one frigate does more damage than 3 artys, lowering defences to "0" in 1-2 turns.
3. Separate units classess for support, melee and recon - seems bad idea. It means, that for a limit of x units per plot as a general rule, you can amass even 4x units of different classes in the same tile . Besides it is illogical, AI can't handle it. I, for example, played game of 2upt limit with deleted additional classess, and it was much more fun, offering some interesting tactical choices. Two mounted units, or maybe archers and pikes on the same tile - for me such dilemma is a solution that joins positives of stacking and 1upt.
4. It is possible to conquer a city with a destroyer (I guess I could do the same with other naval non-ranged units, but I didn't try).
Anyways, it is a great work and lots of kudos for it.