I just noticed that my original link to the Legacy Challenge page is to the generic page, which doesn’t currently include an obvious link to the Sims 4 Legacy Challenge rules, probably because those have only just been posted and are still partly in development (the trait generator in particular).
So here’s is the proper link to the Sims 4 Legacy Challenge ‘Succession Laws’ page, which is where you start. It all sounds horribly complicated when you read through it (or did to me) because there appears to be so much to remember, but in fact there isn’t. Think of the rules as a menu from which you select the three basic elements of your dynasty — what gender inherits, how they’re procreated, and who qualifies first — and that’s the main decision made. The gameplay rules are simple common-sense, and required to create a vaguely even playing-field; they’re probably also the most likely things some people will choose to mess around with, which certainly doesn’t bother me. The spouse rules are simpler than they appear, in that they seem primarily designed to stop you from importing folks willy-nilly and to assure a certain randomness — like marrying someone who was 3 days from becoming an Elder, for instance.
I don’t intend to score my legacy game, because it’s the playing that interests me and I’m not bothered by whatever number of points I may end up with this time around. However, once a player has done a number of these challenges, I can see how trying to achieve a certain score would add to the complexity.
Anyway, my link is now more accurate. Go forth and Legacy! In the meantime, I’ll need to learn to play a large family (which I don’t like) composed almost entirely of men (which isn’t my usual playstyle)…