3 years ago, Google+ was launched in an effort to make Google more social. It's the most successful social service created by Google and the main reason is that Google promoted it a lot and switched a lot features to Google+.
Google Talk morphed into Google+ Hangouts, Picasa Web Albums became Google+ Photos, YouTube comments require Google+, Android reviews and Google Maps reviews require Google+. When you create a Google account, you need to join Google+. There are Google+ features in Google's notification bar and Google+ is the first service displayed in the app launcher.
Google+ was supposed to be a new version of Google, an upgraded Google that's more personal, has better tools for sharing content and better ways to filter information. "This is just the next version of Google. Everything is being upgraded. We already have users. We're now upgrading them to what we consider Google 2.0," said Vic Gundotra 2 years ago.
Vic Gundotra left Google a few months ago and since then Google+'s importance has diminished. Google no longer released some information about the number of active Google+ users and barely mentioned Google+ in the Google I/O keynote. Google+ no longer requires real names, Google Apps users no longer need to join Google+ to use Google Hangouts video calls and there are rumors that Google+ Photos will be renamed Google Photos and will no longer require Google+. "The move would enable the photo service to stand more independently and be accessible for consumers who aren't part of Google+, potentially spurring more growth," suggests Bloomberg.
Google launched some of its best features inside Google+ to attract users. Now it's time to set them free and make them more popular instead of using them to make Google+ more popular.
For many people, Google+ was an artificial barrier. Having to use your real name to write comments and reviews, to share photos, to write blog posts was an obstacle. The Google+ integration improved YouTube comments, but made many users unhappy.
Google+ is not dead, but Google seems to extract the "+" and split into standalone apps and services. The stream could become less important.