I've been using GV (which, was called Hangouts for a while) for years, but never to receive incoming calls intentionally (this would be super annoying).

Rather, it's decent for outgoing calls (free to US numbers) and SMS. Just be sure to suppress its desire to place calls over your cell network if it decides your signal quality isn't up to par (there's a setting for this), and its often necessary to tunnel through a US server.

IME call quality over WiFi is usually okay for accomplishing basic tasks where the receiving party only has a phone number, but the experience falls short of enjoyable.