At first glance Google+ looks like it's about 80% Facebook, 15% Twitter, and 5% Chatroulette!
At the top you'll find the Google+ Bar. With the Google+ Bar, you can "share what’s on your mind, view your Google+ notifications, access your profile, or jump to a variety of other Google products." The notifications were pretty instantaneous and they will allow you to see when someone has commented on a status, added you to their circle, etc.
One thing that differentiates Google+ from Facebook and Twitter, and adds that 5% Chatroulette to the mix is a feature called hangouts. In a hangout you can video chat with members in your circle. The Google+ help center states that hangouts have a maximum of 10 participants, a 90-minute check-in feature to make sure you're still there, and hangouts are not available on mobile devices. You can chat in the hangout (both text chat and voice), share YouTube videos, and of course see webcam video of whoever you've invited to the hangout.