Civilization and Total War are often seen as the big fish in the field of PC strategy games, but for those who are a little more serious about the nuts and bolts of managing an empire, one series often stands above all others: Paradox's Europa Universalis.
Dropping the player into the role of a world leader at the twilight of the middle ages, you're tasked with overseeing all aspects of your people's development through to the cusp of the industrial era, from diplomacy to trade to war and all the fiddly little bits in between.
The last game in the series, Europa Universalis III, was released in 2007. The next one, it's been announced today, is due towards the end of 2013.
Euopa Universalis IV benefits not only from the hindsight brought about in the five years since the last game's release, but also developers Paradox's growing success with other "grand strategy" titles like Sengoku and Crusader Kings II. So in addition to the expected advances - like a prettier 3D map (that now reflects seasons) and improved trade system - there are things learned directly from CKII's surprisingly broad popularity, like a greater emphasis on "personality" (ie the relationships between the 4000 historical rulers in the game) that'll be reflected in EUIV's idea of "Monarch Power".