I got an invite for Google+ recently, before they shut down invites due to apparently insane demand. I have to say I'm impressed. While I have seen stories claiming that its many features are too complex to navigate, I didn't find that to be any particular problem. The menus/buttons are for the most part logically laid out, and everything seems close at hand when you need it.
Circles are awesome. For the longest time I wanted on Facebook the ability to update status just for close friends or family, or to share some geek related post - in fact I used Buzz exclusively for this, since the only people I knew that were on it were geeks. Circles makes that really easy. You can drag and drop your friends into different circles (they can also be in more than one circle, although sadly you cannot drag one circle into another). When you "share" stuff you can select if you want the post to be public or to involve one or more of your circles. It works very nicely.
I also had a quick play with the "hangout" feature. This allows you to invite friends in your circle to a shared video/text chat. On Chrome for Mac I had to install a plugin (the same one used for Google talk), but apart from that it was seemless. I chatted to one friend via video, and a second friend without a webcam chatted along on the text prompt. He commented that the camera switching to the speaker was done very nicely.
Possibly the major benefit for me at least is this integrating into the sites I use like Gmail, Google News and Search. I know that is a controversial step, but for those of us that cannot be bothered to constantly check our Facebook status this is a low noise way of adding notificatons into the ambient background of your daily browsing experience. This may be Google+'s only way of competing with the likes of Facebook. After all they have not had much success with social media given the failures of Orkut, Google Wave and Buzz.
As a clean but featured re-entrance back into the social media game, Google+ shows that Google has learnt many of its lessons. But whether it can attract a following anything like Facebook and Twitter remains to be seen.