Thoughts on GitHub's new theme

The other day, I got a notification on GitHub asking me to try their new website redesign. Now that I've had time to think about it, I thought that I'd make a post on what I think about it.
To start with, the design as a whole feels more modern and a little bit more 'flat'. I'm not sure if this is a good thing or not yet, though it does make the interface feel less cluttered. This makes the content that the interface is presenting easier to digest.
The only exception to this is the top of the repository page, especially the code view (the view that you see by default). Having the different sections of the repository along the top rather than down the side makes it feel like there is more going on than there was before - and it can feel a little bit overwhelming at times. Add to this the new "Add file" and "Find file" buttons, and it really starts to feel rather crowded.
Having said that, cutting the design down to use a single column makes the interface a bit more consistent with the mobile view. This is a good thing - although I found that reducing the width of the page caused a horizontal scrollbar to appear - perhaps it would be better to allow the new design to resize to fit smaller screens? It also opens up more space that can be used to display other things - like the list of a repository's issues, or the network graph in the "Graphs" section (there's a bug with the network graph by the way - it appears to be cut off just before the edge of the box).
Having a single wide column also makes a repository's README (and other markdown documents) easier to, um, read. It makes them feel more like a webpage and less like a file that someone's uploaded, though this wasn't a huge issue for me before.
All in all, GitHub's new interface is an improvement. It's an improvement overall, which makes the interface feel more modern. The top of the repository view feels rather cluttered and definitely needs rethinking.