This isn't going to be a long diatribe on the virtues of Google+ over FB, but just to mention an observation:
The reason people find some intial joy when first enagaging inside Google+ is because of circles, but not because they exist, but because, by starting over with your social connections it affords the opportunity to organize those connections.
I'd venture to say that most people have grown their social networks in fits and spurts and in that process never really took the time to organize them. In the case of Facebook, there also wasn't any (good) facility for organizing them.
Google+ comes along and imposes a new organizational structure onto your social connections that forces anew, the vetting and arranging of your social connections. That disorganized mess of connections that includes family, friends, Christmas card friends, business contacts, high school friends, etc now gets a rebirth, a cleansing in Google+ that feels really good...at first. Like any good feelings, they last for a while, and with Circles you certainly feel more in control of your social networking experience. The shine is off the penny for me. I will continue to use Google+ to explore its differences and to discover content in new ways, but right now its still an experiment for me.
I still find myself not spending as that much time in Google+. It definitely works and can work well. It is an evolutionary step in online social communities, however, my most meaningful connections still remain elsewhere.
