It might be a little dated compared to some of our other entries but Sword of the Stars is still a heavy-hitter and proves (just like some others on our list) that some games only improve with age. At least with this you'll know it won't tax your computer to run it. It combines the RTS combat of Homeworld with a strategic depth that fans of 4X games are all too familiar with. Available cheaper on Steam than the newer titles on our list, it's a solid introduction to the genre.