Love EU4, even though I'm only average at it. Art of War expansion that released a few months back is practically EU5 for all the additions it makes.
If you're going to nab EU4, I'd say that Art of War and Wealth of Nations are definitely necessary.
Yeah those are the big ones. Conquest of Paradise if you want to play natives of Americas or colonizing is too taxing on you. Res Puplica if you want to play the small mechant nations, Venice, Genoa etc. The Digital Extreme edition and Pre-order "pack" could be worth it if you plan to play a lot of Islamic nations (Digital EE) or Byzantium (Pre-order). Oh and the 'Murican Dream if you wan't mess around with the US.
The rest is only visuals or music, visuals were kind of a waste before because you didn't see the units unless you wanted to play zoomed in the whole time, now the battle results actually show those. The music is quite good generally, AoW pack maybe not so much, that I recommend those.
Also, I have a spare CK2 lying around in my Steam inventory.
Is there a easy/smart way to get rid off it here if I don't want to have a PM flood? Also I haven't gifted stuff in a while so I don't remember/know what it gives you if you send it by email.