I have play both civ IV and civ V and i agree with what people said that the best game will be a mix of both.here are my suggestions:
-take out 1Upt but make stacks less usefull:in my opinion the 1upt system doesn't work.the human player has much more advantage than the ai because the ai doesn't know how to use units well.i have found that one easy way to defeat civ V in a war is just to wait in your cities and kill all their units and then counter attack.so please bring back stacking but fix it a bit.big armies should be slow but powerfull while smaller stacks are faster and better at irregular terrain(the bigger the stack is,less defensive bonus it gets from forests).in the stacks the powerfull units will move while hit & run units are more effective separated(more abour that latter).
Also transports should make a return now that there is more than one unit in each title.and take out the cities range attack
Ranged combat:it need a big rework.in civ V is seriously unbalance :melee units are almost useless until the industrial era because they are killed by range attacks.so i suggest that range attacks should be reworked:
-the normal range should be one (except for capital ships and late game artillery)ranged attacks also are less powerfull but still usefull:they can't kill units but reduced their health too make enemies less dangerous against your units
-ranged attacks are more effective in plains than in forest
-explosive ranged attacks produce collateral damage
-if used in cities,there are chances of destroying buildings(only explosive weapons)
Skirmishers vs line troops:apart from the classic rock paper system,civ VI combat should be a bit more mobile adding skirmisher units.this units are weaker than normal units and are worst at defending due being disorganized and are really bad against cities.horewer they have a number of advantages:move faster,retreats and being able to hide in forest with promotions.basically this units will weakend enemy stacks by attacking and then retreating.of course they are just complementary to your main force:most units will defeat then when attacking.in this group there are:ligth infantery,late game cavalary,helicopters and raid ships
More economic control(civ IV tech money )civ IV health and happines system and civ V trade routes should be returning features
I will add more of my ideas latter
-take out 1Upt but make stacks less usefull:in my opinion the 1upt system doesn't work.the human player has much more advantage than the ai because the ai doesn't know how to use units well.i have found that one easy way to defeat civ V in a war is just to wait in your cities and kill all their units and then counter attack.so please bring back stacking but fix it a bit.big armies should be slow but powerfull while smaller stacks are faster and better at irregular terrain(the bigger the stack is,less defensive bonus it gets from forests).in the stacks the powerfull units will move while hit & run units are more effective separated(more abour that latter).
Also transports should make a return now that there is more than one unit in each title.and take out the cities range attack
Ranged combat:it need a big rework.in civ V is seriously unbalance :melee units are almost useless until the industrial era because they are killed by range attacks.so i suggest that range attacks should be reworked:
-the normal range should be one (except for capital ships and late game artillery)ranged attacks also are less powerfull but still usefull:they can't kill units but reduced their health too make enemies less dangerous against your units
-ranged attacks are more effective in plains than in forest
-explosive ranged attacks produce collateral damage
-if used in cities,there are chances of destroying buildings(only explosive weapons)
Skirmishers vs line troops:apart from the classic rock paper system,civ VI combat should be a bit more mobile adding skirmisher units.this units are weaker than normal units and are worst at defending due being disorganized and are really bad against cities.horewer they have a number of advantages:move faster,retreats and being able to hide in forest with promotions.basically this units will weakend enemy stacks by attacking and then retreating.of course they are just complementary to your main force:most units will defeat then when attacking.in this group there are:ligth infantery,late game cavalary,helicopters and raid ships
More economic control(civ IV tech money )civ IV health and happines system and civ V trade routes should be returning features
I will add more of my ideas latter