The ranking system did kind of annoy me. We used G+ heavily inside of Google, and lots of interesting people posted interesting things. As time wore on, I felt like I got less and less of that stuff. A coworker would say "did you see so and so's G+ post" and I would go look for it and not be able to find it until I begged someone a link. I followed them. They followed me. The post had 300 +1s. But I could never see it.
The other thing I thought maybe killed G+ was the "ghost town" effect. Instead of forcing everyone to share everything publicly, people would just share with their close circles. So to an outside observer, it looked like a ghost town, but to the people using it, it seemed perfect.
In the end, I miss it. The people I interacted with on G+ were great. I met some people on the Internet that are now real-life friends. I could always post a random idea or a project I was working on and get feedback. Now I have nothing. Twitter seems like it's a place where people shout into the void about how far to the left or right they are. Facebook seems dead (I never used it). Blogging sites like Medium seem evil. So I just share random things with random friends on Discord. It's sad. G+ could have done so well.