Here's some thoughts/feedback after fighting a industrial/modern war. It was an offensive one for the human player (as I think most are). King/Standard Size/Epic Speed.
Gatling/MG/Bazooka line of units seem to make little sense. Swords are offensive melee, but MGs don't seem to be really useful at all in offense, compared to vanguards and cavalry/tanks. Crossbows updating to these make very little sense, also Strategy Resource wise. As a result, I still garrison cities with Xbows in the atomic age. A defensive unit that takes a resource? No thanks.
Bombard ships are way too powerful against ground units and cities, in all ages. Though part of this comes from the AI liking to embark their ground units when my naval force approaches
But lots also comes from pure power and mobility. In any case, the power of naval bombardments against land targets should clearly go down. Right now they don't support an army fighting on the coast, they annihilate enemy armies single-handedly. Also all Naval Bombard Units from Ancient on up could use Iron (switching to Oil later), and Bireme and Trireme should switch roles/technologies/names (escort ship come earlier).
Bomber units are weak specifically against artillery (due to ranged strengths). This makes no sense, protecting friendly artillery is prime job for AAs and fighters in reality and prime target for bombers. Also good for combined arms game with tanks/bombers being good against artillery, and artillery being good against infantry. Bombers are also rather weak against cities, when attacking cities is a historic big role for them. (Maybe bombers devastating improvements could be one way for strategic bombardment?)
Blitz promotion on cavalry/tanks is a mess due to movement dropping to 1 after the first attack. This "promotion" greatly reduces the mobility of the unit.
Range promotion on aircraft giving +6 is over-the-top, particularly on the Tri/Biplane. More than double the range? This is a promotion I always took, because it gave my planes a global reach across oceans. I think a carrier for ocean crossings would be nice (before jets), making a carrier actually useful, too.
EDIT/ADD: Air unit attacks animation is yawn-inducingly slow. As I recall VEM fixed this back in the day. All ranged animations might actually do with some speedup.
Gatling/MG/Bazooka line of units seem to make little sense. Swords are offensive melee, but MGs don't seem to be really useful at all in offense, compared to vanguards and cavalry/tanks. Crossbows updating to these make very little sense, also Strategy Resource wise. As a result, I still garrison cities with Xbows in the atomic age. A defensive unit that takes a resource? No thanks.
Bombard ships are way too powerful against ground units and cities, in all ages. Though part of this comes from the AI liking to embark their ground units when my naval force approaches

Bomber units are weak specifically against artillery (due to ranged strengths). This makes no sense, protecting friendly artillery is prime job for AAs and fighters in reality and prime target for bombers. Also good for combined arms game with tanks/bombers being good against artillery, and artillery being good against infantry. Bombers are also rather weak against cities, when attacking cities is a historic big role for them. (Maybe bombers devastating improvements could be one way for strategic bombardment?)
Blitz promotion on cavalry/tanks is a mess due to movement dropping to 1 after the first attack. This "promotion" greatly reduces the mobility of the unit.
Range promotion on aircraft giving +6 is over-the-top, particularly on the Tri/Biplane. More than double the range? This is a promotion I always took, because it gave my planes a global reach across oceans. I think a carrier for ocean crossings would be nice (before jets), making a carrier actually useful, too.
EDIT/ADD: Air unit attacks animation is yawn-inducingly slow. As I recall VEM fixed this back in the day. All ranged animations might actually do with some speedup.