Let's start with the promo video, handily hack-embedded by yours truly from the Microsoft servers(!), do enlarge the playback window as needed:
And from the Microsoft blog post:
When Wunderlist became part of the Microsoft family, our mission was to bring the delightful, simple, and elegant daily task experience and build it into Microsoft’s intelligent, interconnected, and security-centric ecosystem to create a new app—Microsoft To Do. Today, we’re unveiling the new version of To Do, which includes a fresh new design, access from wherever you are, and more integration with Microsoft apps and services.
It’s been an exciting journey since we announced To Do. From shared-list task assignments, list groups, and file attachments, to the Mac app and even more product integrations, we took your feedback and created the app you wanted. We’re grateful for your input and the support of both our Wunderlist and To Do communities. We’ve come a long way since those first Wunderlist days and today is one more step in our evolution. Let’s take a closer look at To Do.
We polished the design of To Do by reducing the header size and adding in more color to give the app warmth and personalization. It’s still the simple and elegant app you love, but now with more options to customize, so you can tailor it to suit yourself and your lists. With the new version of To Do, you can choose from a wide range of backgrounds, including the beloved Berlin TV tower that was a feature in Wunderlist. In addition, you can choose a different background for every list.
Want to give your eyes a rest? To Do has dark mode across Android, Windows, Mac, and coming soon to iOS. It’s not just about the backgrounds, though. We freshened up the look of To Do, so it feels simple, yet modern.
There's a lot more in the original post.
Of course, dark mode and other cosmetic improvements were already in the UWP app for Windows 10 (Mobile), so you're not missing everything.
I do worry that updates to the UWP version have already stopped and that some change server-side will break compatibility in the future, but hopefully a) Microsoft will let us know with plenty of warning, and b) that day will be years, not weeks away!
The last update in the Microsoft Store for To-Do was in July and was covered here on AAWP.