The price is tempting, but then… I’ve played a lot of Europa Universalis IV and to me it seems all Paradox games are similar - I mean: too similar to warrant playing EU, IR and CK all together. It’s basically always a map with provinces, that you have to conquer, with some stuff wrapped around that core gameplay. The only Paradox game that’s sufficiently dissimilar is maybe Stellaris, with the caveat, that once the initial exploration stage is over you face a universe divided into coloured blobs that looks… just like EUIV.
So if a friend would approach me and ask for my opinion, then I’d probably say something along these lines: if you haven’t yet played any Paradox game, then pick it up. If you have, better go for another ancients game, like Hegemony III or Field of Glory: Empires.