I have EU4, CK2, Vicky2 and HoI2. I have dabbled in all four but never in depth because I just don't have the time to learn 4 new systems. I am off this summer and want to learn one title in depth. Background: I am a history teacher and have no special affinity for either period. I like all equally. So, if you could only play one for maximum bang for the buck in terms of time investment, which one would it be?