Maps is not an in-car navigation app like Nav. It doesn't have a UI suitable for use in a car, and lacks most of the significant features such as traffic alerting, ETA, alternate routes selection, plan/turn view toggling, and much more. Moreover, the new version of Maps apparently crashes all the time.
It's a breathtaking move on Google's part. Many people, like me, purchased their devices (mine's a Samsung Note 2) specifically because of the excellent Nav app provided on the ROM. People are really upset. No word from Google.