Went back to playing Hearts of Iron 3 again. All things considered I generally, generally, prefer having complete control of every division on the front lines to the "draw a line on the border then paint arrows over it, by the way you can only delegate leaders on a Field Marshall and General level" system of Hoi4. Not just battle control either. Being able to design each division as I see fit is also preferable to Hoi4's template system. I should clarify that I prefer using a mod that makes division composition historically accurate (AKA: actually interesting to engage in) by adding in all kinds of little support battalions to create well-rounded units rather than the default "3 infantry brigades and the occasional support brigade makes a division" system. Yeah Hoi4 is more complicated with it's battalion level division designer, but it never feels as engaging. Hoi4 is in this weird limbo between being streamlined and being complex that may be open of honing by modders but still feels off. Things like the production system, which would feel more impactful if what you could produce was expanded on instead of just 3 or 4 tiers starting in 1918, and I definitely like their air and naval combat system more.
Granted, Hoi3 is shallow in many respects (politics is just window dressing outside of using spies to boost certain parties so that they can win elections and a coup mechanic that's hit or miss, little potential for AH aside from editing the country files yourself or using cheat). This is also extremely niche, but with Hoi3 and prior game's unit picture system you could at least easily add to the pictures yourself with basic knowledge of GIMP to give each unit type a photo corresponding to it's tech level if you wanted. Really helps visualize how your units change as you research better gear. Hoi4's icon system and 3d troop models doesn't feel as in-depth.
Ideally this kind of game would let me edit my armies down to their divisional commanders (portraits optional) like in Hoi3 but have a national focus and air/naval combat system and equipment system in line with Hoi4. But I get it, paradox wants that Casual gamer audience and those loadsamoney from DLCs.
As long as I'm posting this I might as well mention another idea: more "immersive" integration of equipment and manpower to the functionality of ground units. Hoi2's units had a simple mechanic where the number of tanks, trucks, cannons, etc were shown as part of the unit's health bar. Hoi3 only had the amount of men in each brigade and nothing about actual equipment numbers. Hoi4 gets it right with the equipment system and the ability to capture enemy guns in combat or use the loot from a defeated foe. The only real indicator is a flag icon but it works. On the other hand it's limited by the whole template system. The only way you can alter individual divisions is by swapping their template which happens immediately bar adding new equipment. No taking a unit behind the lines to upgrade. Also there's equal application of casualties across all component brigades in Hoi3 and Hoi4. An innovative idea would be to give more options with regards to disbanding units. Instead of sending the whole unit into a nebulous manpower pool, you could disband components into the rest of the division after particularly messy battles or merge depleted divisions into a new one to replicate the kind of ad-hoc formations that say the Germans were rolling with by the end of the war. A division history mechanic might also be included.