I'm familiar with the Paradox titles and I own CK2, so I'll enter in on the discussion.
CKII is, in the simplest term, a feudal rulership simulator. If you liked the high end politics in Game of Thrones, you'll like CKII. It's essentially just another grand strategy Paradox game.
Pretty much.
If you've played Victoria or Europa Universalis, you kinda know what to expect. It's definitely easier to get into than those titles, however, and also more intuitive than CKI.
CK2 is easier to get into than Europa Universalis? As in, more immersive? Because EU is ridiculously easy to get into, IMO. In terms of ease, it'd be EU: Rome > EU III > CK2 > HOI3. Haven't picked up Victoria despite the sales. On that note, you think it's worth getting if I like the other Paradox titles so much? Don't remember why, but I felt kind of turned off by it when I looked into it before.
The family management isn't actually the design base, I don't think (though it is doing the best job of it of any game I've played). It exists because of its importance to the historical era.
Yup. Political marriages, raising children, handing titles to your heirs, establishing family prestige are all important because they were important then. I agree with Grakelin, it does the best of any sort of family management simulator I've seen in a game that's not The Sims (that is, the point of the game isn't family management). EU3 doesn't even have a family management system at all, and EU: Rome's dynasty is more like a nifty screen to look at and imagine means something. CK2 is legit, and a lot of AARs (After Action Reports, basically Let's Plays but usually after the fact) have people trying to get their family in the most prominent position in Europe. I remember looking at one AAR which had the family start out in a vassal kingdom of the Holy Roman Empire and at the end of the game had family members leading several different major countries, a good number of minor countries and were related to most of the other important and non-important people around. The point wasn't to conquer the world or anything, just get the family to control the most power, which is interesting on its own. I'm more for the World Conquers, though (Tuetonic Knights in EU3, doing a "There Can Be Only One: Germany" play through on HOI3).
At $10, I would definitely recommend it without hesitation. At $40, there's no reason not to play the demo for a little while. When it first came out, I pirated it first, and then immediately bought two copies so my girlfriend and I could play together. After getting the expansion packs, I don't at all regret spending over $100 on this thing as I often have with bigger game expenditures.
Although I enjoy the game, I can't just blindly recommend it. It has some serious depth going on that won't be intuitive for you for a good while. For example, I was stuck wondering for the longest time why everyone had more troops than me unless I spent my craptons of gold on mercenaries despite me having more provinces until I realized that you could build structures for each of the locations in a given province by clicking on the right pop-up icons when you click those location thumbnail pictures. That was definitely not obvious to me.
The game is very pretty, though, the UI looks sharp and artistic, the music is good (IMO), the help-screen popups are genuinely helpful (That's like a first for Paradox, I think they actually got native English speakers to write and/or proof their help for once).
The thing is, though, you want to be sure of what you want to do. If you want to forge an empire by carefully managing your own power, orchestrating causes for war and sending your armies out to annex your enemies a few provinces at a time over the course of decades, pick EU3. If you want to forge an empire by expanding into the realms of barbarians, assassinating enemy generals and laying waste to your enemies with your glorious legions while making sure it doesn't go ass-up due to the friction between political parties in your government, pick EU: Rome. If you just want to watch the world burn, pick HOI3. If you want to forge an empire by carefully picking your allies, lieges, vassals and family alliances, fabricating claims on neighboring provinces, hiring mercenaries, participating in holy wars, plotting and executing plots to assassinate your enemies (home or abroad) and holding everything together with the right government laws, selected vassals and personal honor and piety, while constantly reinvesting in what you've already got, pick CK2.
I will say, though, that actual crusading doesn't play that big a part in this game. And it plays a smaller and smaller part with every expansion they release. I can't even remember the last time I went on one.
It can play as much of a part as you want it to. When I formed the Kingdom of Ireland (Which is like how newbies get accustomed to the game, it is the recommended start), I used crusades as ways to expand my empire into the middle east and ended up owning a sizable chunk of the Mediterranean along with gobs and gobs of honor and piety which everyone else respected. That said, you can completely ignore the holy wars as long as they aren't against you or you don't border countries with hostile religions.