This is a great infographic which shows how Google + has fallen flat on its face. They had a good idea, but it was 4 years too late and execution was poor. You can agree, or not with whether it is a success or not when it stands alone. However, when compared to the other social networks, as referenced below, it is not doing so hot.
According to Mashable:
To prove the point, Umpf analyzed 100 online news stories across G+, Facebook, LinkedIn and Twitter. The company then determined the average number of users per 100 million likely to share a story. As the infographic below shows, the gulf between G+ and Twitter in this regard is stark: Only six G+ users out of 100 million shared, compared to 197.3 out of 100 million for Twitter. The difference wasn’t as large for Facebook and LinkedIn, but G+ was still a distant fourth.