I like what appears to be a reduced header and footer. And now the header appears to have useful info instead of just the book title. I also like that I can finally have chapter progress and book progressed available at the same time. (Though I still prefer book title on the top and chapter info on the bottom, that looks to be reversed in the Libra firmware).
What I really don't understand is why ligatures aren't enabled by default in kepubs. That and advanced font control will be about the only things I'm patching once the Libra firmware rolls out to everyone.
Here's a nice review where they talk about the device, but also go a bit in depth on changes to the reading experience.
Kobo Libra H2O Review: Who needs books anymore