With the National Popular Vote bill guaranteeing the majority of Electoral College votes and the presidency to the candidate with the most national popular votes, big cities would not  control the outcome. 

The population of the top five cities (New York, Los Angeles, Chicago, Houston and Philadelphia) is only 6% of the pop. of the US.

Voters in the biggest cities are almost exactly balanced out by rural areas in terms of population and partisan composition.

16%  of the U.S. pop. lives outside the nation's Metropolitan Statistical Areas.  Rural America has voted 60% Republican. None of the 10 most rural states matter now.

16%  of the U.S. pop. lives in the top 100 cities. They voted 63% Democratic in 2004. 
The pop. of the top 50 cities (going as far down as Arlington, TX) is only 15% of the pop. of the US. 
 	
Suburbs divide almost exactly equally between Republicans and Democrats.