It must just be me, but it feels that the site is optimized for mobile browsing. There is very little content and my eyes have to move massively just to read the page. I actually prefer the old layout. :/
Smaller browser widths I agree
But using a phone/tablet to navigate the docs? Might as well use notepad for coding too, since the objective is to suffer.
Plus, though it amy be an unintended consequence, mobile first shouldn't at all hurt the desktop experience, just make sure that mobile is not an afterthought once the design patterns are engrained and it's too late to modify a responsive experience.
Also, I work a lot in Django, and love the new site.