I understand you guys don't want to make a game that players end up hating.
However when you say, you were steamrolled by Russia and then slowly built up again, aren't you actually saying,
"I blobbed like I always do when I play EU3, but this time it only started 100 years into the campaign, and therefore I quit the game only in 1700 instead of 1600 like I always do" ?
I like the CK2 idea that you don't have to blob, that you can have fun even when you are being un-blobbed by fate and by agressive neighbours. You say players hate it, but I get the impression that in CK2 there is a lot that lets you "pull through" and not quit, even when you have to take losses. For example, when you're in a succession crisis with a 5-year old king, or when you have a woman ruler, you suffer, and you may even lose your king titles. But in your head you're like,
"I am weak now, but when my king is grown up (or my queen has gotten rid of the short reign penalty), I will be strong again and I will take back what is mine!" You know, for sure, that your period of weakness will end, because you know the boy king will grow up.
EU3 never had that for me. When you are trounced by Russia or Spain, there isn't that "glimmer of hope" that has you pull through. All you see is, you are losing the valuable colonies, you are racking up debt that takes decades to pay back. You go
"I am not going to get stronger any time soon. When Russia is done with me I know for sure that Portugal will also jump on me and I will end up in a no-fun situation, where I don't know when it will end."
I was thinking, how can you give the player hope, in EU3? How can you let a player see a light at the end of the tunnel, even if the tunnel is still long and dark?
What about having society-transforming events that only kick in, when you are losing?
For example: Cultural "achievements" that happen to you when you are down on your luck, like having a writer compose an epic tragedy that will forever more define your national ethos? (Think: Kosovo Polje for the Serbs... worst defeat they suffered, ever, leading to a very very long time under Ottoman servitude. But it's, like, the supreme epic of their literature, and a point of reference for every Serb even 600 years later.) The effect of such a cultural achievement would be a lasting modifier to all nations that share your culture, and making your provinces of your culture harder to culturally convert / religiously convert after you lose control of them.
You could also have certain military effects, like "Complacency among the officer corps", be removed much easier if you have been through a defeat. Think about how defeats can break the complacency of your ruling classes and totally shake up your nation. Think Prussian reforms under Hardenberg and von Stein, after Prussia's crushing defeat at the hands of Napoleon.
Other things... bankruptcy could lead to improved business practices. The greatest scholarly minds are inspired to write ground breaking treatises, after disaster befell your country. Would France ever have become the leading nation of the enlightenment, if the French monarchy had not lost all its prestige under Louis XV and XVI? Playing a successful absolutist monarchy should PREVENT you from ever seeing much enlightenment! Seeing your monarchy lose all its prestige in lost wars and bankruptcies, on the other hand, could trigger the event that gives the player hope again - "Our philosophers are developing a totally new system of government." and you know, if this keeps up, you will be the first to get to try out the revolutionary republic concept! If you choose to tolerate the new thinkers, that is. You could also try to crack down on them.
Religious things as well... having conversion forced on you by a stronger nation, could lead to a resurgence in cultural thought where your great thinkers re-define what it means to be an Omani / Portuguese / Brandenburger. Religious could suddenly become less important to your nation, thereby giving you that "
The central idea is, that after defeats and during periods of weakness, some really grand things happen to you. While you are down on your luck on one front (bankruptcy + lost war) a light appears on another front (breakthrough in philosophical thought). When it's darkest (loss of all colonies) your nation realizes that there are totally different pathways to light and fortune (emergence of national consciousness). When you think you lost it all (death spiral of debt and instability, revolters forced your government to make concessions that destroy all advances you made in centralization) you suddenly see that the failure only aided you in shedding the parts that held you back (the weakness of your government provides your merchants and producers with unexpected freedoms, your economy recovers, you discover you like constitutional monarchy much better than absolutism after all).
I think EU4 would profit, as a game, if there were rewards for those who accept failure and pull through.
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The game would also gain unexpectedness and challenge. A nation that you defeated and stripped of half its territory might get "Rise of Nationalism" and suddenly be stronger than it ever was, despite being cut in half.
Think of how France made it through the 18th century, if seen through the lense of EU3: Started out as a blob under Louis XIV, won phenomenal successes (imposed its dynasty on Spain, colonized N.A., became immensely prestigeous), then declined massively (lost all N.A. colonies, lost all prestige, went bankrupt, suffered massive revolt) and then soared again like a comet after the string of defeats totally shook up the country's government, economy, national identity and ultimately its entire self-definition. It should be fun to play through something like that.
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Modifiers that you get only during defeats, and paths of development that only open up when your society suffers a deep "Shake-up", would enable something like that.