I hate the left hand side design that they've taken. It'd be different if they had some content to fit in the extra space they've freed up, but the content that should be the main focus of the page has been pushed to the back seat.

I think it's improved quite a bit over the years. It's a very clean design.

The design they rolled out within the past few designs to me is a bit cluttered, and goes against the typical crisp/clean Google design.

I like the actual video pages. They're very clean and the video takes the front stage.

I hate what they are doing/have done to the logins.. I deleted my youtube account a while back, and now I can't create another one without signing up for Google+ too and using the Google+ account name next to stuff :/

I do like how they finally got rid of that bottom-toolbar thing for video playlists. I don't know why, but that made me very uncomfortable.

It's now on the side of the video. Example: https://www.youtube.com/watch?v=0pXYp72dwl0&list=SP196C0077CA9AE008&index=2

Yes that is actually very nice. I like that you can control the playlists more conveniently now.