Numbers-wise, this doesn't look to be that big of an update, but quite a few smaller issues have been addressed.
If you're using a European hosting provider with rather strict file permissions, and were having some difficulty getting Armadillo setup initially, you'll (hopefully) be very happy with the changes we've made. Armadillo now uses an entirely different approach to creating the media folder where all your uploaded images and other files are stored, which should be compatible with more hosting configurations and make things a lot smother.
On the Responsive front, mobile users with smaller devices like the iPhone 5S should enjoy the interface changes which reduce clutter and prevent overflowing text.
Several localization adjustments have been made for the Dutch, German, Polish and Swedish versions. Swedish users should also see their blog date in their native language.
Of course, this is a free update for all Armadillo 2 users, and it should appear for you when you next start Stacks. Enjoy!