Following Victoria 3 dev diaries. The social, economic and even diplomatic simulation seems reasonable, maybe the implementation will be underwhelming but the design direction hasn't been to dumb them down and there are several promising changes, such as:
- The political struggle is between Interest Groups such as industrialists, trade unions, the clergy, the Armed Forces, etc.
- The diplomatic crisis system has been remade into the centerpiece of diplomacy
- Wages according to a labor market
- Flexible building and production system allowing industries to change their ownership, workforce composition and inputs; this isn't exclusively for production but also for services, bureaucracy and anything modders will think of
- Rigid and nongranular National Focus system replaced by bureaucracy and authority resources
- Bilateral trade with supply routes instead of an unified global market without any transport involved
- A country with an illiterate population can have a significant number of scholars and catch up with the rest of the world in technology, but won't be a technological innovator
Some bad decisions, too, such as the cookie-cutter UI.

The big draw, however, is the military system. They've gutted on-map armies and tactical movement and replaced it with what looks like the dullest AI controlled frontlines I've ever seen, with very little player input. And despite stating their goal is to make war more strategic, their mobilization system brings only modest improvement compared to Victoria 2's and still isn't a realistic simulation of conscription. The naval system is better than Victoria 2's but that's no achievement, the predecessor was barebones. The new war system doesn't even feel like dumbing down the game to a broader audience, it's too dry to appeal to anyone; it's a certainty that they'll introduce some deeper combat with a DLC. The least they could've done was to implement some version of HoI 4's frontlines.