Why do you feel it's lacking. The Nexus 5 has the infinite homescreens, the OK google, holding to access widgets, wallpapers, homescreens, and the same feature of dragging an app to add a new homescreen. And OK Google, opening apps, and using Google Now and google voice is flawless. I see and experience no lag. I've heard some people say the apps are a bit bigger and I've noticed it too. The only thing I notice when I first launched it was a little bit of the screen was black for a moment. Never any problems since. Or are you referring to the dialer option not being there?
I used to swear by nova and loved it on my phones and some tablets. But I think Google Experience Launcher is better.