75% off the base game (nothing exceptional about that) but also 75% off all DLCs except the latest one (Holy Furry). DLCs haven't been more than 50% off since 2016. You receive Steam codes, but if your Paradox account is linked to Steam, they will activate automatically. Pagan Fury (a new music DLC, also the band's name) is also 75% off but isn't listed on the sale page: https://www.paradoxplaza.com/crusader-kings-ii-pagan-fury/CK…
If you are interested in a modern recreation of pagan Northern European music, I recommend Wardruna and Heilige (the latter is incidentally the German word for healing, but this isn't tame New-Age music). You can watch an Heilige concert on Youporn: https://www.youtube.com/watch?v=h1BsKIP4uYM&feature=youtu.be
The DLC's have always been a day one purchase for me (how un-ozbargain), so I never played close attention. But I'm pretty sure the DLC's are always 75% off every major steam sale/paradox event, except for whatever the latest one at the time is.
Not that it matters. I've put it over 5000 hours on this game! It may seem expensive at first, but it's great value if you put the time into it.