I prefer the one notification and nav bar at the bottom with the nav buttons over on the left under my thumb and the notifications on the right under my other thumb. 4.2+ puts the nav bar at the bottom with the buttons in the middle  far away from any of my fingers and the status bar up the top. It just wastes space and is not as functional to my mind. Seems some people like it and some don't. Google did it to bring the phone and tablet UI's in line.