You only need Internet to start the console for the first time and to install games, even if they are on discs. That was a bit weird but it's fine. Sometimes I play Xbox One offline and it works perfectly fine, once the games have been installed. I don't know how was the Xbox One user interface before, but the current one is the best of the generation, in my opinion. Everything is logically organised, it's easy to navigate and remains quite simple even with lots of games installed. I'm loving the Xbox One UI.
You have also a lot of Internet options and statistics so you can check your connection for online play, etc.
