If you prefer Civ4 over others, give Old World a try. Many of the same people involved, most notably Soren Johnson is also the lead designer of Old World, and the game brings many new ideas to 4X.
Disclaimer: I'm one of the team members. In our experience, most people who say Civ4 is the best Civ end up really liking Old World. When it comes to Civ5, I personally find myself agreeing with Sullla.
Disclaimer: I'm one of the team members. In our experience, most people who say Civ4 is the best Civ end up really liking Old World. When it comes to Civ5, I personally find myself agreeing with Sullla.