I think I've put enough hours into Europa Universalis IV to give a bit of an assessment. I've only played as Castile (the Iberian Wedding event did not fire for me), and as I've learned to do with Paradox grand strategy games, I put the game on easy difficulty to start, as there's a ton of new mechanics that takes a few hours to learn. France or England don't need to declare war on me while I'm still learning where to find things.
In terms of quality, it's very similar to CK2. At least in my experience, I like CK2 better. The problem with EU4 is that once I started colonizing, that was all I was looking at. Europe became an afterthought, and there's so much available land to colonize, that I never really felt like I needed to bother any of the major powers over their claims. I understand that there's a way to play a generated map, which could be interesting.
In CK2, you have your titles, and you're trying to move up in the world. Claiming more land doesn't come free, and you can either use a CB, or play the strategic marriage game.
You could play EU4 as a conqueror, but you're letting rivals get stronger because they're the ones colonizing, and you generally want to go wide instead of tall in these games and just blob as much land as you can.