One UI made its global debut last month, getting set up to replace Samsung Experience on all Galaxy smartphones and tablets. It won't be released until 2019, but you should start understanding what the South Korean company wants to accomplish with its new user interface.
Rather than packing in too much color and animation, One UI scales back to focus on what you need and making all interactions feels as natural as possible. Samsung has long been criticized for its industrial-like user interface; however, its replacement appears to be simply modern. There aren't stacks of menus and buttons to jump through.
Samsung reminds everyone that, with the new user interface, its hardware and software are "working together in harmony." It'll take some testing to understand that, but the naked eye can tell One UI blends in well with the premium build quality of Samsung's mobile devices. One UI seems mature and refined.
Here's the promo video, courtesy of Samsung:
The beta program was introduced in November, and it shouldn't take too long for the public built to start rolling out. Samsung expects to issue the software update to the Galaxy S9 sometime in January. After the 2018 flagship gets set up, the Galaxy Note 9 will be next. As for the Galaxy S8 and the Galaxy Note 8, both of those high-end phones are on the list to get One UI as well.
Samsung's Galaxy S10 will undoubtedly ship with One UI, too. The next flagship should be announced in late February and released within a few weeks after that.