Lego City Undercover is pretty much exactly what its title says it is: Legos, in a city, starring an undercover cop. This may explain the name change, but we'll just let the above E3 video do the explaining for us.
For the first time, the fan-favorite LEGO City vehicles and play sets come to life in LEGO City: Undercover, exclusively for the new Wii U console. Players assume the identity of Chase McCain, an undercover detective armed with clever disguises. The mission is to put a stop to the fiendish Rex Fury and end his crime wave in LEGO City. As players run, drive and even fly through the city, they’ll use the Wii U GamePad controller as a new police gadget.