Better gameplay.

1. I like having fewer but more distinguishable units. Ever since Medieval, the number of units keep going up but the differences between them have become so minor that they have really become indistinguishable from each other. Empire had different stats for all the different line infantries of each faction but the differences were mostly too minor as to be worth bothering with.

I like the days of Shogun and Medieval 1 where units mattered. There really was a big difference between the elite units and the peasant units. Stuff like having spears or swords or armor piercing weapons and the like mattered. There was also a noticeable difference between fast and slow infantry and fast and slow cavalry. There were also clear differences in the cost and upkeep between the better units and the lower ones.

2. Fewer but more varied maps. Ever since Rome, the tactical battles were done on the tile were the defending army was on. That meant that almost everything was flatland. I'm so tired of fighting on flatland all the time.

STW had bridge battles, the occasional two bridge battle, battles with choke points, multiple hills, mountains, forests, etc. I used high ground, bridge and forest advantages all the time on Shogun and Medieval 1. I've barely used them on any Total War game since. I don't even remember any bridge battles post-Medieval 1. I haven't lured any cavalry to forests, either. It was all flatland.