(Disclaimer: This all will admittedly be subjective)
To build EU5, i would first define what is the core of eu4:
- The ability to start as any nation in the world and improve upon your starting position with war, diplomacy, colonization, ...
- Replayability with different ideagroups and starting nations, alternate paths to world domination (2 different individuals can play the same country and end up in a vastly different spots)
Then i would define what worked well as a mechanic in eu4:
- Ideagroups (The balance can be off but the system as a whole works very well)
- Nations with their different government forms, national ideas, strengths and weaknesses, flavour, ... (For example my favourite nation austria plays vastly different than brandenburg, despite both being in the german culture group and in the hre)
What worked somewhat but should be improved / overhauled:
- Make trade more dynamic (Making your own trade routes, Having more influence with a monopoly on a trade good, ...)
- Technology could be earned passively instead of actively (Would be hard to balance but with the game being built from the ground up its doable)
- I would still keep mana in the game for filling out idea groups, but i would make the aquisition less rng-dependant (There will always be a need for abstract resources in this game)
- Colonization feels bland (I can´t put my finger on why that is, but it feels tedious to do and could be much more enticing)
What didn´t work well and should be scrapped and replaced with something completely new:
- States / Territories
- Corruption (Especially corruption from territores)
- Revolutions and the late game in general (I know that the late game will never be the focus of the game, but the only runs i played to the end in the last year where world conquest runs)
- Rebels (Most uf us take humanist and offensive to not be bothered with them and other pdx games have shown that there are better alternatives to display disloyal provinces)
- Mercenaries (How they are now, we will see how they are in the next patch, but it doesnt look that promising to me)
Many people in this thread proposed farreaching improvements to the internal and peacetime mechanics in EU5. While i agree that it should be made more engaging than it is now, the essence of the EU-Series was never about characters like in ck, or about the economics and simulation of the population like vici.
Most of all i want a polished, working product at the release.