The problem with Google Hangouts is that it's fragmented. The GMail client does have external connectors, in fact they're still free for Canada/US calling. But calling another person for a hangout still requires they have Google+, IIRC.

Google has a chance to destroy Skype with GTalk and hangouts, but instead they're suffocating it by trying to bundle it with Google+. I don't mind signing up for Google+, but I've given up with using Hangouts with my parents because they don't want to sign up for a social network.

If/when WebRTC hits mainstream, it's conceivable that built-in video chat won't matter anyway. If I can generate a URL and send it to anybody with a browser and start a video conversation, I don't need a heavy client like skype any more.