I think people dislike Google+ as a social network because it's forced on you. If you make a Google account, you have G+, if you want to comment on youtube or whatever, you need G+. Nobody cares about G+.
Honestly social networking sites in general feel useless. I haven't opened up my FB in a very long time - I have my chat synched with an app, which is the only reason I even have it in the first place. If we all switched back to AIM I wouldn't even notice the difference.
Mentioned before that Twitter feels a little meh just because I don't tweet as things are happening to me, then forget to tweet about said things afterwards. So that's meh.
I guess what it comes down to is that people aren't going to want to keep track of one more social network. For all the garbage Facebook includes - and there is a LOT of garbage - from an objective perspective, it did this shit first. That's why it's so popular, that's why nobody cares about other social networks like it - even if they're designed better. Then couple that with it being shoved down your throat because Google does want one of their projects to gasp fail, and you have a recipe for annoyance.