I have a Lumia 920 and I find the turn-by-turn navigation to be abysmal. It gives distances in yards and the vocabulary does not extend much past "keep right", "keep left", and "follow the course of the road". It's also flat our wrong more often than not where I live. Google tells you street names and exit numbers, which is vital in large metropolitan areas.

Also, map searching is no where near as good as Google Maps.