The navigation assistance in my car is significantly better than the one Google Maps offers. For one thing it doesn't lose its mind every time I go under an overpass. For another, the UI is vastly superior: it shows me the distance to the next waypoint prominently in the center of the display, between the speedometer and the tachometer. When approaching a turn, the same area of the display is used to show the configuration of the intersection, even complicated ones like double forks or t- or y- shaped intersections, or even acute turnbacks. My car never barks orders like Google Maps does. If it needs to say something, it is awfully polite, saying things such as "If possible, make a legal U-turn." And finally my car's navigation responds to a voice command to stop navigating, which Google Maps doesn't seem to know.
In my experience the only thing Google Maps navigation has going for it is superior data. I really wish I could have my car's UI with Google's data.