This is what a question on MSE looks like on my phone, with left nav turned off:
For comparison, here is what a question from a site that doesn't yet have the responsive design looks like:
Long comments are especially annoying with the new design; short lines mean more stuff gets pushed out of view. Even questions are kind of frustrating to read with all that extra indentation; the current mobile view puts the voting buttons next to the title, above the body, so that the question can have the whole width. Further, I bet that when the indented post links are joined by "mod" and "start bounty" like in the second screenshot, that line's gonna wrap.
In a small viewport like a phone, please use the page width better.