I have used Google+ for about a week and I like it. Compared to other social networking solutions I found it instantly useful, with a clean design. When I started using Facebook it took quite some time to get a grip on what the benefits was for me, but for Google+ I didn't have to look as they were very visible directly.
Features of Google+
Circles is almost perfect, they let me organize both people I know and people I want to follow (Twitter style almost). This helps me to be able to easily be able to filter the stream of information in a very good way.
Circles would be almost perfect if it also was possible to filter the posts on keywords/tags like you can do using TweetDeck by creating a column that only shows posts containing the hashtags/search terms I decide.
With the combination that those filters would only work on the people added to that circle, it would make it a very powerful information filter.
Hangouts I haven't really tested yet, but they do seem to be video chat made right for social networking. I just hope they will add a few features so they are easier to discover. Right now they will just show in your streams and are thus easy to miss. A feature to list all ongoing Hangouts in your circles would be a great addition.
Also, being able to easily create a private hangout, that is only visible and accessible for the people you want to be in it, would be nice to have.
Sparks looks like something that can be very useful, but at the moment it is to limited in what it will discover. For sure it should be possible to use Sparks to discover posts on Google+, filtered on circle(s) or not of course.
Media integration is simply done right. Images, videos, sounds, links and so on are so easy to add, heck you can even watch a YouTube video together in a Hangout, and they are displayed better than with any other service. Enough said!
The Toolbar integration is another thing Google simply done right. I work a lot in Google Docs, and seeing the red notification indicator alerting me from there is just right. Even better, I don't even have to leave the document I work on, I can +1, reply, add to circles, etc directly from the notification dropdown. So simple and so right.
That is probably also a reason why there seems to be more activity on Google+ during work hours, people simply get notified while in Docs...
I didn't use the Notifications option under Stream until yesterday. Mostly because my experience from other services is that it usually was a waste of time. Buy do I regret not testing it quicker.
Default it gives you a similar list of items related to you as the notification dropdown in the toolbar. Then, clicking on the More option top right, you can also quickly filter the lists as you wish. This is making it virtually impossible to miss interesting discussion and other stuff related to you.
It is also going to make it incredible quick to catch up on everything if I have been away for some time and have loads of notifications. I will then be able to everything from that list(s) without having to click around forever wasting time.
Beyond First Impressions
There are still a lot of quirks for Google to sort out and features missing, but so far I am extremely impressed about what I have seen so far. Judging from what others are saying, that seems to be what almost everyone that has got in is as well.
Maybe I am a little overexcited though. After all, I had very low expectations after the previous big failures Google had with Orkut, Buzz and Wave so it wasn't hard to be impressed. I don't think I am though, Google+ just seems to be right in every part this time.
One reason I believe that Google+ will give especially Facebook a fight is the easy access we now have to the people working for Google. Before we only knew they names of a selected few from Google IO and other public events. Now we have easy access to practically everyone within Google to follow.
Best part is that the Google people seems to be as enthusiastic about that as we are. I have seen +Vic Gundotra hosting public Hangouts for example.
I think this is brilliant and I am sure this is going to be a great resource for Google to keep improving it very quickly.
Unless they, against all odds, manage to really screw things up, Google+ is from now on my primary social place on the net. Facebook I barely use besides keeping in touch with people, but they will soon move here too. Twitter on the other hand still will be very useful and are not as threatened as Facebook, but over time and when more people joins Google+ they too are at risk, especially if they don't start making money soon...
So, without doubt two big thumbs up to Google+ from me, or maybe that should be a gigantic +1?