Worst thing ever. Sure there’s a few upsides, like the threads are better organized now, but that’s overshadowed by the horrible mistakes they made:
Liking a reply to a comment will add a like to the original comment as well. So if someone says something incredibly offensive like “kill all the jews”, and someone replies telling him to shut up and gets 50 likes for it, “kill all the jews” gets 50 likes on it. This means rude or offensive content is much more likely to be brought to the top, and normal comments with few replies are sorted to the bottom.
The google+ integration means that you see a lot of comments that completely blank, because whenever someone shares a song without an additional comment it’s added to the normal comments for the video. This also means there are a lot of comments just describing the video without actually commenting on it’s content.
On top of that, you have to deal with new virus links, offensive ascii art, and a community more full of trolls now that the clunky system has driven off everyone who wanted to use it for legitimate purposes.
I’m sorry for the rant, I used to use youtube a lot and since I refuse to integrate my channel with google+ I have had to stay out of my account permanently.