Hearts of Iron 2: Doomsday
Hearts Of Iron II is the buck-toothed geek genius of real-time strategy games. Sure, it looks like its had its head flushed in the toilet, but underneath the unspectacular surface is a thoughtful and intricate war game that manages to balance a daunting depth with a good level of accessibility. As long as you don't go into it expecting a few quick skirmishes and awesome 3D battle scenes, you'll enjoy getting your fingers dirty.
Die Doomsday expansion includes the full game at half the price, and adds six years to the timeline (now running from 1935-1953). Nuclear weapons move = into the fore in later years, although E their destructive power is reigned in a r little for balance.
There's also a scenario editor, tweaks to the AI, and HOI's active fan community have directed a number of other improvements to balance. Doomsday is a great chance for you to catch up with a game that's improving with age.