I want to point out one thing: On CK3 many paid features of Ck2 have become vanilla features (playing with anyone who is not Christian, bloodlines, reforming religion etc), with hoi4, instead they have almost everything wrong: They have removed a lot of features excellent present on hoi2 and hoi3 to put others badly done (see the horrible world tension, which replaces single person belligerence, too few spies, searches with ho2 tech teams that were wonderful, the economy where you really traded with resources for other resources, using civil industries ...) If with Ck3 to D1 they have done wonders, with hoi4 they have messed up almost totally (the only real upgrade, besides the graphic one, is that of the puppets, which can be annex and which have levels, for the rest too many steps have been taken back)