Space Empires IV, the ultimate 4X space game, is out and getting very good reviews.
GamesDomain.Com’s reviewer notes that there is a pretty steep learning curve — this is definitely not a game for Civlization and Masters of Orion veterans, not 4X newbies.
For fans of the genre, however,
otherwise, there simply isn’t a deeper and more challenging space 4x game in existence. The grand epic feeling of the game is hard to miss and you really feel like you are running an empire.