Attention AOE 4 devs:
Most important: ZOOM LEVEL. AOE 2 DE has the best zoom level, but it could still be better, i.e. it should be possible to zoom all the way out to view the entire map if desired. AOE 3 DE has the worse zoom level, even at ‘very far’, the buildings are still huge. I have no idea why this was done, especially when AOE 3 has the ability to zoom out more but was restricted for some reason. Some people have large screens, they should be able to zoom out as much as they want to. Some people hate scrolling the map around constantly. Some people want to spectate a game and be able to see everything at once. Some people prefer the look of a whole bunch of smaller units and buildings as it adds to the epic scale sensation. Commentators too appreciate the full zoom out feature. Personally I dislike scrolling and like to play on the most zoomed out level possible to minimize scrolling. I have friends who wont even play because they hate scrolling and they prefer playing an RTS with less/no scrolling.
Variety of units:
AOE3 got this right, AOE2 did not. In AOE2 all the civs are very similar, and often you will see only crossbows and a mangonel or two in a game. No matter what the civ is, its very often double archer range feudal. I have to try to think of interesting fun ways to deal with mass archers, to try to keep the game interesting, because I know thats what I will likely face. In the feudal age, ALL units are the same, they even look the same (except eagle warriors for meso civs). It is so boring. AOE3 has saloon units, civ specific unique units, home city cards and card that send unique units, unique explorers, etc and each civ is distinctly different with different units and way more civ specific unique strategies. And also, the action starts quicker, and the feudal units, because they have variety, and more fun to play with and civ differences come into play immediately.
No forward castles/towers
Again, AOE 3 and age of mythology got this right, but disallowing building too close to enemy tc, AOE 2 did not. Disallow cheese strategies like towers/castles on opponent starting resources. Many AOE2 games around the 900-1200 range revolve around people building forward castles on one of the defenders gold piles, and it shoots down economic/tcs/farms also. It is an overpowered strategy, which is why it is so so common, and it is too easy to perform and too hard to defend against. And also it is not enjoyable to play against at all.
I hope the devs take these ideas into consideration.