There are two main directions I would ideally like to see explored more in AoE4 relative to AoE2, though I don’t consider them very likely given what I’ve heard so far. They are (1) more clearly defined towns and (2) some mechanism of town annexation.
Consider the word “Empires” in the series title. To me, an empire means having multiple towns and usually annexing rather than destroying any town whose defending forces you’ve defeated. On the first point, in my experience, most players’ entire territories tend to look like one big village. Obviously, you can have multiple town centers, but it’s not often clear where one town ends and another begins.
On the second point, the defeat of an enemy army doesn’t give you control of their territory, nor does just collapsing certain key buildings, like an original town center or central castle. Once you’ve killed off all hostile units and even razed any means of replenishment, you’re basically left with a bunch of defunct and useless buildings to either ignore or tear down. You’re not left with newfound control of a still functional town and possibly any remaining villagers, nor do you even get a raise in your population limit, for instance (since the enemy won’t be needing his population allotment anymore).
I think you could technically use a monk to convert them one by one, but that would be really tedious.
For a game that seems to pride itself on historical accuracy, these two broad features have always seemed to be the least realistic aspects. As I understand it, the Middle Ages were generally a period when a castle and/or fortified town determined control of an entire region around it, including the more rural infrastructure within. If any part of this “province,” for lack of a better term, was threatened, the local lord would send out troops from his castle to defend it. Take the main castle or hub by either killing or starving the defenders, and the whole area is now yours, including the existing structures and often even the people already living there.
I’ve seen some hints that AoE4 might be taking a step or two in that direction, so I’m eager to see what they come up with. For whatever it’s worth, if it were up to me, here’s how I might do it.
Define a radius around a town center or castle that is under the TC’s or castle’s protection. Maybe give it a default value that can be modified (within reason) by enclosing the desired area in walls. Make it so that if that TC or castle is destroyed by an enemy, every structure (and possibly every civilian unit) within its zone of protection automatically belongs to that enemy. Perhaps tweak the population limit to accommodate the player’s new serfs/vassals, since they’ve likely just acquired some extra housing.
This would likely require some balancing revisions, but something like this would achieve a basic improvement in historical verisimilitude and make the game more fully deliver on the empire-building implied by its title, but at the same time, little if anything else would change, so I don’t think the game would be too fundamentally altered. I welcome other opinions and/or ideas, though! This is mostly just fantasizing with a bit of speculation thrown in!
Much of this may just be my inner Sid Meier talking, but I think there’s at least one game, Rise of Nations, showing that it is possible to marry the overall structure of the AoE series (and thus most or all of the things we love about it) with one or two key enhancements inspired by the likes of the Civ series.