Now that the power curve has moved in favour of the player (4 extra legions, additional defensive options), can I suggest some tweaks to enemy units and defensive abilities. Not sure what is possible, so I've put a variety of ideas below.
change unit stats so each enemy unit & civ is properly differentiated now, instead of having mostly identical stats currently (e.g. Picts should be harder than Gauls as they were never conquered, Pergamum archers should be stronger as currently spawning with 70% archers trivialises their invasions, Goths should have stronger cavalry, and so on)
Add ability for invasions to spawn a third unit type. Currently you only ever need to build two types of legions as enemies only spawn with 2 of (archers, cavalry, infantry, special). Even if there is no unit art for e.g. Carthaginian Archers, you could use pergamum archers and handwave it away as "mercenaries"
strengthen walls. I suggest maybe +50% to +100% hp as it doesn't currently seem "fair" that an infantry unit can destroy walls in a few seconds. Strengthening the stone walls would also help differentiate vs palisades.
allow multiple enemy types per map (e.g. Carthaginians & Numidians)
add bonuses to Roman cavalry damage & defence when moving to attack (the opposite of legions who get a defence bonus for standing still)
add javelin unit defence when moving
Tweak projectile damage on a per-civilisation basis (e.g. boost Pergamum archers)
Caesar sends cavalry and javelins (maybe 10% each) in addition to legions
Edit: I would probably add, most of the above changes would make invasions weaker overall (with rare exceptions for enemy civs that got buffed), but I do think they'd be great for flavour. Compensate with higher invasion multipliers perhaps.
Now that the power curve has moved in favour of the player (4 extra legions, additional defensive options), can I suggest some tweaks to enemy units and defensive abilities. Not sure what is possible, so I've put a variety of ideas below.
Edit: I would probably add, most of the above changes would make invasions weaker overall (with rare exceptions for enemy civs that got buffed), but I do think they'd be great for flavour. Compensate with higher invasion multipliers perhaps.