The responsive design is very nice on pages like the homepage (has a theme, more buttons on the top than mobile) and has extra functionality on questions (view votes) and the asking UI (all the formatting buttons unlike mobile).
I really like this version of the site. However, on things like Chat, it is non-existent and having it in desktop mode makes the text quite hard to read and I have to zoom in and scroll.
Please set the responsive design to be the default style rather than the mobile on all pages that have it in a form that works, i.e. questions, the homepage, asking questions, tags, maybe the editing UI, and more that I don't think of.
It's pretty effective on the flags page, too, which would be nice if it were linked on the profile on mobile, too (not super relevant...