It's not a radically different look, but things are definitely more streamlined and there's more room for video to shine. That said, there's at least one big, oft-requested feature everyone can try now: dark mode. As the name suggests, it turns all of the white UI elements and backgrounds black, which definitely makes video stand out more. People who don't always go fullscreen while watching videos on YouTube will definitely want to give this a shot. Between a simpler UI, bigger video thumbnails and redesigned channel pages, the whole experience feels different but still familiar, a good goal to shoot for when redesigning such an important part of the internet.
A few changes are coming to the iOS and Android YouTube apps, as well. Perhaps most notable is that you'll be able to control playback speed, just as you can on the desktop. Another big change that YouTube says will roll out soon is a more adaptive playback window -- this will let videos shot in portrait mode or in a square aspect ratio use up all the available space on your screen to display properly rather than show up with big black bars. Given that portrait video isn't going anywhere, any change that makes videos shot like that easier to view is probably worthwhile.
Lastly, YouTube is taking this opportunity to unveil a new logo and icon. The red box that has long surrounded the "tube" part of the logo is now being moved out to the left, with the signature "play" icon showing up in the middle. Given that the red box with the "play" button has been used as YouTube's icon in various places (including the app you'll find on your phone's home screen), it makes a lot of sense to incorporate that into the main brand's logo as well. At the very least, it'll likely be a less controversial new logo than the one Google unveiled a few years ago.