In the political aspect HOI3 and HOI4 are absolute opposites, each one terrible for their own reasons. The former because you cannot have an ideology switch at all unless you keep switching tags with the console to use espionage on yourself with another country and also maybe having a 2% chance to coup another country with espionage maxxed (which changes absolutely nothing historically, enjoy communist Romania joining Barbarossa on the side of Germany); the latter because politics is made of "press button to turn Japan into a proletarian dictatorship in 1937" and "choose decision to restore ridiculously anachronistic state".