In my experience, Google Maps is really terrible outside the United States. It doesn't seem to understand that in the UK, a narrow country lane might have a speed limit of 60 mph, but nobody could ever drive that speed on it. It's constantly proposing insane detours off A roads onto back lanes obstructed by sheep and farm equipment.

Unlike Citymapper, Google Maps doesn't have a notion of multimodal transport: cycling to a train station, for example. Citymapper also doesn't "lose" your in-progress journey if you click the wrong thing or close the app.