An early build of BB10.3 leaked with more features and a flatter look
TL;DW - flatter UI, more unique UI elements, removed boxes around app icons (thank god(s)(?)), more features in stock apps, disappearing bottom bars when scrolling, red accents (unconfirmed for retail release).
I personally thinks it looks nice. It's just an early build, but I hope they keep refining and adding to the OS.