I have played this game for about 15 years, if you count HoI2 - and it is basically the same game but with many improvements. It's much, much, much better than HoI3, not to mention the beyond repair mess that is HoI4. Probably has a steep learning curve, but beginners can start with for example USA and get used to the interface before jumping in to the war (or getting jumped on around 1941-1942). I have not experienced the lag issues other mention on Windows 10, at least not in fullscreen. And the guy who mentioned that he claimed Germany... that is simply not possible. You can only claim your national cores, and the UK has 0 national cores in Germany. Maybe some mod or the acceptall cheat? Or if it's a bug it's something I've never encountered in at least 3000 hours of playing (again counting the original HoI2). Also, this is kind of two games in one - DH full and DH light which is closer to the original HoI2.
