On the downside you are now required to link your YouTube channel to a Google+ Profile or Page to make a comment and Google+ notifications aren't really a substitute for your YouTube Inbox. And even for Google+ enthusiasts, the new commenting system will take some getting used to.
Here's a brief overview of my first impressions some of the features and drawbacks of the Google+ commenting system:
The Good: better moderation options, longer formatted comments, communications managers and more
Better Moderation Options
I think one of the best features of Google+ comments is the ability to easily block posters and prevent comments that contain specific words or phrases.
To manage who can comment on your channel and videos, open the comment settings for your channel (www.youtube.com/comment_management). There you can approve or ban specific users, or block comments containing specific keywords.
You can still require moderation of comments before they are posted, and turn off comments for individual videos, either in your comment settings (www.youtube.com/comment_management), in the settings for your video or in your default upload settings (www.youtube.com/account_defaults).
You can require approval for all channel comments too by selecting that option in your channel navigation settings.
The Google+ spam filters are also pretty good at detecting potential spam comments. When a comment is flagged by the system as spam, you can review it to decide whether to let it appear on your video or not.
And you can mark comments as spam and report abuse directly and ban commenters from your channel by clicking the little down arrow to the right of a comment:
You can learn more about reporting abuse in the Google+ Help Center.
Longer Comments, Basic Text Formatting, Links, and Editing
If you are wordy like me, the 500 character limit for YouTube comments could be seriously constraining. With Google+ comments, there is no limit to the length of your comment. Longer comments will only display the first few sentences with a "Read more" link, so they won't take over your comment page.
Google+ also allows some basic text formatting, although there aren't any fancy text editing tools, so you have to remember the formatting code:
Asterisks to bold text: *bold* will display as bold
Underscores to italicize text: _italics_ will display as italics
Hyphens to strikethrough text: -strikethrough- display as
Hard to remember? Bookmark this Google+ tip sheet.
And now you can also include a link in your comment to another video or a website. Links to YouTube videos will be converted into the title text.
And if you made a typo or thought of something new to say, you can edit your comment after it's posted. Just click the little down arrow to the right of your post.
Shares of your video on Google+ will appear in your comments, and your comments will appear on Google+
When someone shares your video on Google+, their post (and any replies) will appear on your video watch page as a comment. That means that you can see what people are saying about your video even if they don't post a comment on your channel directly.
Also, when you post a new comment you have the option to share the comment on Google+ as well. If your comment is deleted from the video watch page, it will still be readable on Google+.
If you don't want your comment to be shared to Google+, be sure to untick the "Also share on Google+" option, which is currently on by default.
Communication managers for Google+ Page-linked YouTube channels
If your YouTube channel is linked to a Google+ Page, you can add a user as a "Communications Manager" for both your Google+ page and YouTube channel.
A communications manager can post and manage comments, review notifications, and organize your Google+ circles of followers. They can't change any settings, upload or delete videos or view your channel's analytics.
The Bad: Limitations to Google+ Comments
Google+ is now mandatory to comment
The biggest limitation to Google+ comments is that you and your commenters need to sign up for Google+ to use them. While you can continue to use your YouTube channel identity on Google+ (no "real name" required!), and you will only rarely need to visit or use Google+ directly, it still means you will have to create a Google+ profile or page to continue commenting on YouTube. All your fans and friends will have to sign up for Google+ as well to continue commenting on your channel.
And beyond the Google+ requirement, comments made using the old YouTube system are now effectively orphaned, because there isn't any way to reply to them directly. As time passes that will be less of a problem, but right now it can be pretty frustrating to be unable to respond to comments made less than a day ago.
Your comments are no longer in your YouTube Inbox
And even if you are keen on the idea of Google+ comments, it can take some getting used to a new and different system which isn't always intuitive to use. For example you will no longer see notifications of new comments in your Inbox, but instead will have to find them in your Google+ notifications.
When a comment is left on one of your videos, instead of getting a notification in your hard-to-find YouTube Inbox, you'll get a Google+ notification right at the top of your screen when you are viewing your YouTube channel.
Notifications of the latest comments on your YouTube videos will be marked with a small YouTube icon to distinguish them from your other Google+ notifications (and admittedly this isn't likely to be an improvement if your channel and it's linked Google+ Profile or Page gets a lot of notifications). You should also be sent an email notification from Google+.
Unfortunately Google+ notifications don't create a nice archive of comments and replies, and that feature of the YouTube Inbox will probably be missed.
The spiffy new comment features can be used for evil
But beyond that, many of the great new commenting features - posting links, the ability to edit posted comments, increased visibility of shared links to your videos - can be used as tools by spammers, haters and harassers. I am hoping that improved blocking, moderation, and spam detection will improve the overall quality of YouTube comments, but only time will tell if that's the case.
The Ugly: linking your YouTube channel to Google+ and the new comments can be confusing, complicated, and occasionally buggyIt's clear from the frequent posts and questions from confused users that linking your YouTube channel to Google+ can be a confusing and complicated process. And beyond that, sometimes it doesn't work the way it's supposed to. That's why I started this blog!
Google+ comments themselves add an additional layer of complication, and still have some kinks that need to be worked out.
If you are having trouble with the new commenting system or Google+, there is help!
Post your question in the YouTube help forum or the YouTube-Google+ Integration Community or contact YouTube support directly. Hopefully someone there can help your channel be straightened out.
And here are some useful Google+ resources to get you started learning about how to use Google+ itself: