Strive to become Ruler of the World by establishing and leading a civilization from the dawn of man into the space age, waging war, conducting diplomacy, discovering new technologies, going head-to-head with some of history’s greatest leaders and building the most powerful empire the world has ever known!
This game is less "complex" than its predecessor, for example religion was removed, instead of getting civics through research there are seperate "policies" which will unlock by accumulating culture, and happiness is calculated on a national level instead of per city, which is something I personally don't like that much.
There are some other changes that I do like though. For example the 1 military unit per tile mechanic. No more stacks of doom and more tactical gameplay. Archers and other 'ranged units' that didn't have a real ranged attack before being able to truly do a ranged attack is also a plus.
Civ V is easier to learn than Civ 4 (which is the only other Civilization game I have played) because of its decreased complexity, while it still has the "one more turn!" addiction factor. I personally would have like to keep the more 'complex' features, but it is still a great game.