And so Google+ is being shuffled off into oblivion, like many other useful or semi-useful Google services before it. I was on it for a couple of years, but didn't post much there. By the time it arrived I had started using Friendica, and the decentralized networks were just more interesting, more anarchic, and a lot less corporate.
The thing about the security issue with Google+ mentioned in their blog post is no doubt real but also a red herring. I expect that whoever is in charge of these decisions was just waiting for an opportune moment to announce the shutdown of the service, and a security bug is a convenient event on which to do that.
My main memory of that system was something which became known as the nymwars. Google tried to copy Facebook's "real names" policy, and that had some pretty bad outcomes. It was obvious that in the quest to become the next Facebook Google was prepared to throw some people under the [Google] bus. At one point Eric Schmidt went on the record to say that he didn't care about anyone who wasn't able to use their "real" name, and that people in at risk categories should just get off his platform. It had been known for at least two decades that consistent pseudonyms don't lead to the kind of bad behavior which was claimed, but advertisers (Google's real customers) wanted the "robust social graph" based upon names which they could cross reference against other banking and purchasing records from data brokers. It was an example of where the interests of Google's users and their customers came into conflict.
Google+ never really got any traction in the social networking field. The technology was ok and a few people found a home there, but it was centralized and proprietary and so not of much interest to people like me. It was used by some "open source" people who I thought ought to have known better, but that's probably because their business interests were closely associated with Google or that they were working there.
In the unlikely event that there are any Google+ users reading this and wondering where to go next, I'd recommend that they get an account on a fediverse or Hubzilla instance. Those systems can't be arbitrarily shut down, and you can run the software yourself rather than just being another SaaS victim. Proprietary software service dependency is a problem, and anyone who claims to believe in open source should be practicing what they preach.