I have some thoughts about balance. I also think that there should be more realistic changes.
First of all: First-strike ability of ranged and gunpowder units. These units should damage the melee enemy before the melee combat and power of "first strike" should be calculated using the ranged CS. Mounted and armor units should have the "Ignore first strike" ability (like it was in civ4). In this case mounted units will be more important for taking down archers/Xbows.
Gunpowder units should have the "First strike" and ranged CS with the range of "0". They will not have ranged attack but use their ranged CS for "first strike" and additional protection against arrow-based attacks. Musketeers should be a little weaker, but have the first strike. Also, from this point of view, legionaries should have 11 melee CS and 0-ranged CS with "first strike" (
wiki: Pilum,
wiki: Testudo formation).
Mounted units should ignore or nearly ignore (like 1.25 terrain cost on hills instead of 2) terrain cost, but have the attack penalty on rough terrain. In current situation cavalry is almost useless - you almost never have enough place for the manoeuvre.
Musketeers should cost less hammers than logswordsmen. Knights should be stronger but also cost iron additionally to horses. Cannons should require iron.
Renaissanse-era cavalry should be completely reworked. There should be 3 general types of cavalry:
1. Cuirassiers - strong (stronger than riflemen) but slow cavalry with penalty against other cavalry. Main purpose - killing the enemy infantry on the open terrain, acting like a tank.
2. Hussars - fast and weak cavalry. Main purpose - killing cannons, finishing wounded units, pillaging roads and improvements, scouting. Also, this will be the good reason to include Poland as major civ (I find it really shocking that there is no Poland in Civ games)
3. Dragoons - fast cavalry that gets defensive bonuses and generally acts like the rifleman while in defense. Main purpose - catch cuirassiers, protect vulnerable units from hussars, take key positions fast.