I'm a big fan of Crusader Kings series, but have never put any serious effort into Europa Universalis (although I admit to salivating when I saw the world map in EU3 + all expansions). Are they very similar? Is it worth sinking 50+ hours into EU?
I would say CK2 does not differ all that much from EU3. Lots of unique mechanics from the original CK, for example, the need of prestige for declarations of war and throne claims have been scrapped in favour of more EU-esque design choices,
much to my personal dismay but oh well.
Dynastic politics are much more abstract, raising armies and researching technologies is much more straight-forward. The map covers the whole globe, you can opt to colonise, send merchants to trade centres, endorse or oppose the reformation
among other things you will need to take care of depending on your country of choice.
Compared to EU2, EU3 is much more of a sandbox, which would later influence the design of HoI3 and Vicky 2. If you want a more deterministic and historic experience in the vein of HoI2 you might want to look up For the Glory, a total conversion commercial mod of EU2 and arguably superior to the original. It also looks like EU4 will be less of sandbox and more like EU2 regarding country events. The original EU has largely been made obsolete by its successors. Paradox also made some Scandinavia-centric proto-EU games in the 90's, I never played them though.