Had some issues downloading and launching the installer even this morning, but just tried again and it worked fine.
Initial impressions on my Mid-2014 MBP are that (having upgraded safari already), changes are limited to mainly cosmetic and UI design, which in a way, is good news given the movement to ARM-based architecture signalling a potential convergence with mobile devices that could have taken things down a different path... That said, it does seem like the whole UI has more padding around everything, so actually there is less space on the screen for content. E.g. safari top bar is larger, more padding around the dock icons etc. To me, that indicates that there's maybe an intent to enable MacOS to support touchscreen interfaces.
I tried to reduce the overall UI scale to compensate, but it gets pretty laggy and buggy when I do that. I'm putting that down to the Intel Iris graphics not really having the horsepower with all the other UI effects going on. Seeing slow scrolling in safari and laggy video playback. Moving back to 100% scaling and everything is normal again.