The thing that distinguishes G+ is circles, which is actually a terrific idea. I have very little use for Facebook, but I use G+ for non-public communications quite regularly. (I won't call them exactly private, since the communications are still being mediated, and archived, by a centralized social network.) However, as with many other examples of technology, technical superiority doesn't mean much of anything with respect to widespread adoption. Facebook is the de facto standard, even if it sucks.
For me, and I would hazard to guess quite a few other people, the thing that makes G+ useful is that it failed to be adopted as a social media standard. I'll miss it when they finally turn it off.