that comic strip really does sum it up.
Circles - easy to add people into them and group people. Sharing is only done amongst these circles, so no more worrying about comments from family on dodgy status's / pics etc.
Photos - sharing photo's in specific circles, so if you are tagged within that circle in a photo, your entire friend list won't see it, but rather only the select circles that share it. this way you can keep those photo's who you want to share with friends and those with family completely seperate with ease.
Privacy - you can preview privacy settings on how select people will view your profile, nice way to make sure there are no privacy loopholes.
Adding and removing to your circles - it's not compulsory to do it on both ends. So it almost has a twitter feel to it, where you can follow people without them following you back vice versa. Also grouping people is easy, so say you have a forum friend, and they become a really close friend - just throw them into the appropriate circle.
It is easy to use, feels more interactive, it isn't cluttered with crap or advertising or apps, it is content driven.
Your feeds are seperate, so you can view your entire circles feed, or click on the different circles for just that particular feed.