Whether any Europa Universalis game is fun to you depends on how much you like or dislike the basic game loop: Pause the game, fiddle around with a huge number of settings for the country you control, unpause, and wait what happens. Of course, if for example the setting you changed was a war declaration on your neighbor and you sent an army his way, things will happen rapidly. Then you pause again, adjust your orders, and unpause again. In other phases of the game, you will only do minor adjustments, and you might let the game run unpaused at higher speed for a while. This is the gameplay of EU4, of other Paradox grand strategy games like Crusader Kings or Victoria, and it will be the gameplay of EU5.

Somewhat more particular to Europa Universalis games is another cycle: While you aren't absolutely forced to play that way, in many cases you will want to grow your country by military expansion. This is a cycle, because once you have conquered some land, there are game mechanics that will stop you from further expansion for a while: You will have a truce with other countries, neighboring countries will be angry about your aggressive expansion, and you will need some time to integrate the lands you conquered into your country. After some in-game years, the truce will have run out, the neighbors calmed down a bit, and you dealt with internal unrest, so you can start expanding again. This cycle will most certainly exist in EU5, just as it existed in EU4. But the detailed game mechanics that rule that cycle will be different.

That gets me to a probably controversial hypothesis of mine: If you have played EU4 100 hours or less, you will possibly enjoy EU5 more than if you played EU4 1,000 hours or more. My argument for that is that pretty much everything you can learn by playing EU4 for more than 100 hours is specific to EU4, and will not apply to EU5. It does not help you to know that at the start of EU4 it is a possible strategy to give away all your crownland to the estates in exchange for one monarch point per category per month, as EU5 doesn't even have monarch points. It is very likely that EU5 will have some systems in place that address the same fundamentals, e.g. a system that prevents you from having too many alliances. But knowing the details of how that works in EU4, and how to increase your possible number of diplomatic relations, is probably not going to be relevant in EU5, as the system will be different.

So my advice to other EU4 n00bs is that you shouldn't worry about not being an expert in EU4 when deciding whether EU5 is a good game for you. It will be the EU4 experts that will complain the loudest about EU5 after release, because they feel the changes more deeply, and might prefer certain game mechanics from the previous version.

I am looking forward to installing EU5, choosing some country more or less at random, fiddling with some settings of my country with very little expertise, and the unpausing the game and seeing what happens. From the very fact that I can choose a tiny country or a major power, I know that this isn't a balanced strategy game. Conquering the world isn't the only possible goal, and steering a small or middle sized country safely through the centuries might actually be more interesting. A good part of the fun is not knowing how everything works at the start, and finding out through your own experience. If you are open to the experience of Europa Universalis V, and you aren't too stressed about not knowing everything from the start, this might be a game for you.