Civilization V has a large assortment of nation leaders to choose from that have an even bigger assortment of scenarios that are able to play out for said leaders. Each game can be quite unique in this way as each leader allows for a different nation to be controlled.
Policies are used as a tool to gain a variety of customizations that benefit ones society. There is a branching tree of policies that will allow the user to pick certain aspects that will suit them best such as adding law or religion to ones society which will give gains in certain aspects.
Civilization V has a great combat system that feels very tactical over previous versions as there is no stacking of troops, but with the new hexagonal grid players can surround enemies as well as allow for better tactics when planning attacks.