Collections is like following random Pinterest boards created by other people. I don't know about others, but I like to follow official things, or things that have the most followers but none of that info seems to be surfaced. Featured really means nothing to me. Is it hand-picked? Randomly generated featured? Are they paid to be featured?
Communities are cool but it's really hard nowadays to beat the communities in subreddits. Anonymous users seem to give a lot more to the community in an unselfish manner vs. Google+ users seem to post in communities in a self-promoting manner. This could just be anecdotal and my subjective viewpoint but that's what I see.
I honestly don't know how Google can do social, but I'm glad they're trying different things. Hopefully they try something new.
Random thought: I find Slack very similar to Google Wave.