My initial reaction to G+ was a negative one. It was so immediately reminiscent of Facebook that my distaste for that service was evoked, and my gut reaction was to run away. It took a lot of reading about the improvements over the Facebook platform, from sources I feel that I can trust about such considerations, that I decided that G+ was worthy of a fair trial. Ultimately G+ and Facebook have the same objectives; they serve the same basic social function. They even go about it in the same way for the most part. If you're a Facebook user you will intuitively understand G+. The differences really are in the details and execution. It's never been the functionality of Facebook that I have minded, but the behaviour it inspires and it's intrusiveness. By extension I have no particular issue with the intentions of the Google offering; and while I'm generally not a fan of Google's privacy practices in G+ they really are leading the way (more on that later).
G+ has notable features comparable to other social networking platforms. Most obviously (from my perspective) from Twitter and Tumblr. It has Twitter's approach to opt-in content and the circles feature mirrors Twitter's lists in this respect. Tumblr is mimicked in the ability to 're-share' the posts of the people you are watching with the people who are watching you.
Circles are G+'s distinguishing feature. A circle is, simply put, a categorisation of the people you are following. These categorisations can then be used to filter the content you are viewing but more importantly to restrict the visibility of content you post. If you upload a photo and set it to only your family circle, only members of that circle will be able to view it. This is a winner in terms of privacy but also grants you the kind of flexibility that would otherwise only really be possible by utilising multiple Twitter accounts. This is Google's big privacy win, not only posts, but personal details and profile elements can be assigned circles individually. It's an intuitive and granular control over who can see and access what information about you.
Despite it's positive elements I won't be maintaining a Google+ account, but would recommend getting a beta invitation to anyone who is interested in a Facebook alternative. There are a number of features clearly missing such as support for businesses and groups but I'm sure these will be added in time.