When the new DLC comes out, I like to discover, how huge impact new mechanics have. Intelligent agencies, reworked supply system, new docrines mechanic, peace deals - everyone on paper sounds complicated and overhelming, but I think I don't have spend more then hour to look basic stuffs, I think. German Reich is always a good choice, if You want to know, in which direction things are going, because it is Your choice: when You want to start a fight, against whom, who is You allies, etc. If You have playing for vanilla now, it is a good moment to add mechanics from DLC's, because a lot of them are a game changer. One mention: I'm playing with all DLC's from years and at least from BftB I was buying new DLC in the day of premiere, so it is hard to say for me, witch mechanics were adding to vanilla, and which are implemented just with DLC, but my advice: try to learn spies first. Thanks spies:
- You get a nice bonus to the naval invansion (against UK for example);
- You get a bonus as well, if You break a cipher from Your enemies;
- thanks collaboration goverment You can finish against the Soviets with taking just a european states of USSR.
I think, learning NSB is more "natural", because You have no choice and You have to use supply system, division templates, army spirits and doctrines, but I think it will come with time.