One of the complaints users of Google+ have had (and notably, something Tech Crunch is whingeing about) is the lack of "brand pages". Right now, only actual people are supposed to post to Google+. Google has said that brand pages are coming soon.
Over the past two years, brands have spent immense amounts of money to build followers for the Facebook fan pages. One of the dirty little secrets of this is that while it's great to be able to follow the customers that do choose to "like" your web page, having a lot of Facebook followers doesn't drive that much traffic back to your site, and it really doesn't drive much new traffic.
So along comes Google+ and the +1 button. Right now, folks aren't paying a lot of attention to the +1 badge. But Google's already started incorporating the data from it into their search results, both at the social ("your friend +1'ed this") and global ("+1 by #### people") level. If they haven't figured it out already, brands will soon realize that if they get their loyal customers to +1 them on Google+, it will act as endorsements when those customers friends come across the brand in a Google search result page.
There's any number of other great things about Google plus (Circles) and a few not so great things (it's kind of boring right now.) But I think that brand pages, +1 and Google search are the "killer feature" that will carry Google+ from a remarkable launch to a true Facebook rival.