Google Maps works. The only thing I'd say is that HK can be complicated to navigate as a city: many malls with multiple stories and footbridges connecting them at different levels, and that can be difficult to see or understand completely on a primarily 2D app like Google Maps. But there's not really a good app for mastering this 3D environment that I know of.

For restaurant reviews and bookings, sometimes OpenRice has more available, but a lot of it is not in English. The photos can be helpful though. Can look at this on web too - app itself not strictly necessary.