Vicky 2 (with updates and expansions) is the best of the PGS games at domestic matters; you can have an interesting Vicky game without ever declaring war. Which is good, because man are the war mechanics not particularly interesting. Probably the weakest out of any game of the series, in the sense that its more of a pain in the ass to manage without being any more interesting. Anyway, every country has access to raw resources, and populations that want raw and refined resources; you can get better access to raw resources by adding secondary powers to your sphere of influence, and produce refined resources by building factories. You're racing to gather prestige, industry, and military might (all three of which are highly important). If you do well you get to be a Great Power and Exert Influence over Lesser Peoples. Which is great except people expect you to get involved in random conflicts that have nothing to do with you and you end up fighting world wars because some dirt farmers decided they wanted their land back from Russia. If all that sounds fun, yeah, its worth buying.
Oh, and there's an internal politics management system where you and your populace have differing ideas about whether that Marx fellow was right in the head. And sometimes you fight over it. I can't decide if its an amazing system or a frustrating and useless one; the fandom is mixed. Still, there's some pretty great alt-history stuff possible like Anarchist USA vs Facsist CSA. Although most of it won't happen without player intervention.
Unrelated, but. I kind of wish Parodox would make some kind of fantasy/post-apocalyptic/something-punk/otherwise not real life game where they shoved together much-simplified versions of Crusader Kings' dynasty management, Vicky's soft power/economy/prestige, and Hearts of Iron's combined arms warfare. All of those games are really really good at one thing and kind of weak in the others. With the exception of HoI which is weak at everything except war but its the only game were the war isn't mindless deathballing so there's that.
Or more plausibly, a game that combines Vicky 2's domestic system with HoI3's warfare and makes both of them significantly more usable and comprehensible, that would make me very happy.