It wouldn't be YouTube if things weren't drastically changed every now and then. It can be jarring, but hopefully it leads to better use cases of the site and overall more satisfaction.
The most current case: YouTube Leanback. A new version was just released, this time focusing on helping users find content they want to watch, and then keeping them satisfied with both more videos from a single stream and an easy browse experience to discover related streams. At the moment it's a work in progress, but it meets all the expectations and use cases of the initial version with the added benefit of easier navigation. There are more ideas on the way though, hoping to help surface more common, but simple, actions for the user as well as providing discovery of better videos.
You can check out what's changed, or as always go play around with it yourself.
Might I suggest though: sign up and log in to YouTube. You'll get more things which matter to you personally that way.