PC Gamer
You get a beautiful, thrilling wargame out of that bargain. While I found a number of flaws when I stood close to the tapestry, it's important to remember that Hearts of Iron 4 exists to encompass the whole sweep of the war. It captivates me because—imperfectly, impressionistically, and perhaps a little amorally—it lets me orchestrate the most titanic armed struggles in history, from the fussy economic details to the cut-and-thrust of mechanized warfare. There are other great strategic-level wargames out there. But I have never played anything like Hearts of Iron 4.
IGN
Hearts of Iron IV is a strong contender for the title of ultimate armchair-general game. The biggest problems I can point to are almost all performance-related, putting a slow, frustrating finale. This one’s well worth the extensive time investment required to learn how to manipulate its myriad moving parts into a well-oiled engine of war. Hearts of Iron 4 wields complexity like a swift armor division during the blitzkrieg, allowing it to serve the idea of layered, cerebral, strategic warfare instead of letting it needlessly bog down the experience.
Polygon
Hearts of Iron 4 lets players win or lose WWII on their own terms. For now, after many dozens of hours, I'm taking a break from Hearts of Iron 4. Not because I'm sick of it; quite the contrary, in fact. What I need to do is some serious reading, some planning on what my vision for the United States should be in 1936. And when I've done that planning — when I've formulated my character sheet, as it were — I have the utmost confidence that Hearts of Iron 4 will be ready for me to play a role in world affairs exactly how I want it.