The pacing of the game has been overhauled, including the entire tech tree. Shirk and Beach's team have tried to make sure units have a usefulness for a much longer period of time, a worry of mine because adding new units such as "Great War" biplanes and machine gunners would have been very difficult to play with if it kept the pacing of vanilla Civ V.
"The entire system of how units come out, the pacing, the cost, all of that stuff has been reworked," Shirk said. "If you look at the tech tree, there has been a lot of shifting around. We always wanted to get at least one tech level between each unit in the chain. We don't want you to get musketman here, and the very next tech you can get will give you a rifleman."