Themes are their own section in settings now. The presets are still there, and on top of whichever one you pick you can set your own accent color with a real color picker, shade the greys with a background tint, and change how round everything is. Your changes sit over the preset rather than replacing it, so switching presets keeps your accent.
You can change the fonts too, for the interface and for headings separately. Pick one of the six bundled families, name any font already installed on your computer, or load a .ttf, .otf or .woff straight from a folder. A loaded font then appears in both dropdowns like any other. If you move or delete that file later, the app notices and goes back to the preset's font instead of listing one it isn't actually using.
Memory is down a lot at idle. The app hands heap it isn't using back to the system, keeps WebKit's caches on a much shorter leash, and decodes the blurred background artwork at a fraction of the size it used to.
The home feed no longer gets slower to scroll and hover the more of it you load, because shelves that are off screen stop being painted. The three-dots menu on a row also used to open in the wrong place the further down the feed you went, sometimes far enough that clicking it looked like it did nothing.
Enjoy customization, tinkering with fonts was my favorite thing.