PC Gamer lists both Galactic Civilizations II and Sins of a Solar Empire in their list of the best strategy games on the PC!
Galactic Civilizations 2
"If you’ve ever wanted to conquer space with an army of customisable doom-ships, this is the strategy game for you. It has smart, creative AI, and a full-size game can take weeks to complete."
Sins of a Solar Empire
"Sins captures some of the scope of a 4X strategy game but makes it work within an RTS framework. This is a game about star-spanning empires that rise, stabilise and fall in the space of an afternoon"
Read more at PC Gamer: http://www.pcgamer.com/best-strategy-games-on-pc/