It's stark, and it emphasizes the metadata in comments over the actual content.
The biggest mistake in that re-design is assuming Helvetica Nue and Arial are good design choices. They are crunched together. Both are harder to read compared to the current Verdana title and body text.
For a minimalist site like HN, Verdana is the ideal font for readability. I prefer the current style. To be honest, 99% of what makes HN work is the choice of Verdana.
It was my impression that usernames are deliberately de-emphasised on HN, and I have come to see the reason for it and like it.
Hate the zebra stripes. The yellow bg-color on the even-numbered rows leads me to believe that those stories are more important than the ones in odd-numbered rows. Like everyone else said, in threads, the metadata is over-emphasized.