1. When I log into stack overflow, the status bar at the top usually contains information I want to know.
2. The use of negative space is better, but the question title and question body seem to be too separated from each other. The question body looks too much like an answer, and their isn't enough differentiation between the two. In the original design, the tabs and the line clearly separate from the answers.
3. He seems to have gotten rid of a lot of the statistical information about the page. I use this information to decide on the value, relevancy, and recency of a question. It's kind of like Github, one of the first things I do is check the network graph, and see how healthy a project is.
4. The votes are too small in his new design. This is a critical aspect of the site, and allows visitors to make snap value decisions. It should be large, it's at least as important as the entire body of the message.
In general, his design looks better and is less busy, but would kill the overall usability. Stack overflow is useful because of the information density, not in spite of it.