Marshall Kirkpatrick also likes it:
Big picture take-away: Google has built an attractive, intuitive, intelligent service that’s fun to use and speaks to a deep human need for contextual integrity of communication. There is not just public/private, life is more complex than that. This need, unmet by almost any other social network today, is where Google is aiming to win the hearts of users. The app the company built towards that aim is smooth and pleasing to use.