I'm liking the new changes for the most part, but there are a few little things that I'm not too big a fan of. Mostly with the story map.
Scrolling by clicking or holding the middle mouse button no longer works for diagonals, as it seems to lock in on whichever direction (horizontal/vertical) the mouse moves in first, which makes navigating feel a lot clumsier and more awkward than it was before.
And to be a bit more nitpicky... The new look of the story map feels a bit bloated compared to the previous one. The 'bars' for each chapter are thicker with more empty space above and below the text than in the previous design, so it now takes more scrolling to move past the same amount of chapters. The thin gap between them also doesn't help with that, breaking up the more compact and seamless feel it had before. That gap looks to be about 1mm (on my screen, at least) which means that a story map with 1,000 chapters in it would have a full meter of extra scrolling for no real reason. But that is a bit more of a personal preference.
And the default grey of the 'read' chapters is also a bit hard to distinguish from the background on the white site theme. It looks fine using the black site theme though, and the sepia one too.
Beyond that, I also miss the arrow buttons on the main page (for the recently updated stories, new stories, and notable stories lists).
Also, I've found a very small bug with the new in-story sidebar:
The [name • ## chapters] box that shows up when hovering over one of the authors' profile pics in the 'Contributors' section appears behind the sidebar, if the sidebar is brought out by clicking the little button for it (when you're zoomed in enough or have the browser window take up only one side of the screen as I usually do).
It works fine if the window is maximized and the sidebar is naturally open though.