Circles was a great idea. But not really good enough. I'd have liked an "ignore" circle, like banning users on other platforms, just quietly, like the shadowbans some implement on a personal feed level.

Also, Circles was the only good thing about Google+. The rest was average to bad, and the forced integration into all kinds of Google services, the forced realnames, and the lack of third-party integrations killed any kind of goodwill/benefit-of-doubt anyone might have had.