I’ve been invited to Google plus this morning and haven’t gotten off it since then. So I would say it is a nice take on social sharing. Google has hit a better chord than facebook in a lot of features and it has took lessons from the buzz blunder and other social networks. Features seem to have been given a lot of thought and work fairly well considering its being field tested.
Even though its fairly simple to use, you somewhat need a little social networking experience to get started with it. I’ll assume you know how facebook, twitter and orkut(optional) works with this whole post…
I’ll talk about the features which are interesting and somewhat different from facebook with Google plus

Animations and intuitive UI

G+ is really fun to use with fun little animations. You can click, drag, box-select, and do really a lot with drag and drop, specially with circles. j,k keyboard shortcuts work like gmail.

Circles

You can call it an step up from Facebook groups. I am tending to define it more on lines of a cross between Orkut (yes that site is still up :P) Groups and Facebook Groups with a lot of more pep in it. Also where facebook lets you arrange people in groups, Google makes you do it. Which helps a lot on the site later on :)

Hangout

Talk, video chat with upto 10 people at a time. you can also watch youtube videos together. lol I can almost hear Skype saying  “Goodbye cruel world!” ;) Ankit and I took it for a test ride and found some glitches which will probably be fixed before a full scale public release. Watching youtube videos together is awesome :D

Sparks

This is a completely new feature which makes plus different in all respects from other social networks. Add your interest and see content from the web related to it. I am hoping in near future, they start considering open graph data (yes, its an fb initiative but a really good way to let people categorize their content) for putting up stream for that.

Stream

Where most people consider it a copy of facebook feed, I see fundamental differences. These differences are that of design. If you do not know this, you can filter your facebook feed according to status updates pics etc etc and also by groups (click the arrow near most recent or whatever you have previously selected and see).  Posting to stream also gives you options to send it to various people. “Public” behaviour is more like twitter, so when you share something as a public post, anyone on plus can respond to it. So share it to “Your Circles” or “Extended circles” instead for only limited people.
Do checkout the “Incoming” tab for people who have you in some circle and you have not added them to any circle yet. it may turn into a spam house soon enough but you may find interesting people before spammers come up on the site

Tagging people by @/+

Though we have this feature in facebook too, it behaves more like twitter and somewhat worse than it. you can tag people with + or @. @ gets converted to + so for me you have “+Piyush Mishra”. When you start typing, it starts giving you options of people as autocomplete and that is where it starts to suck in my opinion. You can start typing any random name and tag the person. And the person probably gets a notification for it.

Reply Via Notifications

You do not need to be on G+ to respond to all posts on your or your friends streams. You  can do it from the top Google bar anywhere. Now this would be super awesome if they allowed the bar to be placed on other sites as well via an API (probably then I would call it an FB killer)

Edit Comments

I am yet to figure out if this is a good feature or a bad one but yes you can edit your comments and prevent further possible shame in a lot of cases. though it may disrupt the flow and logic of most conversations

Ultimate balance of Privacy

This is where Google probably strikes gold. They have tried to and in my opinion made a really good balance of privacy this time. You can disable comments on posts, disable re-share, select exact people to public while sharing, circles and tagging. all are awesome ;)

Data Liberation

Google is giving out your data. proabably one of the only social networks allowing a proper version of this :D

I am eagerly waiting for the developer API to get released!!

I am yet to test photos and others. do comment with any tips etc so that I can add them to this post ;)

Edit: For a complete user and feature guide check out Google+ Tips and Tricks doc-cum-wiki