Big Sur so far/I tried it and it seems fine.
I'm one of those brave souls who impulsively upgrades their OS as soon as there's a beta out*, so I've been running macOS Big Sur for a few days now. Here's a quick summary of how it's going!
*It's not that brave since I don't actually run any of my development environments on my Mac.
New UI Styles
The new look is great. I know some people are going to hate it, but honestly it's something fresh and I'm here for it.
Some apps (notably ones that didn't look great before) look not great with the new styles. The iTerm2 preference pane somehow now looks even more cluttered and messy than it did before.
While I have nearly all notifications disabled (except for my calendar notifications) on my desktop, I do much prefer the new style. Not sure what it is, but I never liked the old notification appearance.
Bartender and the Menu Bar
I'm a huge fan of Bartender 3. The macOS menubar can easily fill up with junk and it makes it super easy to only show the stuff you actually care about while still allowing access to the rest of the cruft.
Sadly, it sounds like they're working on a core rewrite to support Big Sur as it doesn't really work at all currently.
Karabiner Elements is another victim to these issues. They apparently need to make some pretty serious changes to how it works to support Big Sur so we might be waiting on that for a bit. It seems like Hammerspoon works just fine though, so you might consider moving your customization there.
Fortunately, I had a programmable keyboard I could switch to get my custom bindings back and I'll shortly be switching to the new Keyboardio Atreus which I'll be doing an article on!
Three or so processes crash every time I try to join a call... but then it still connects. I'm sure some update will fix this.
I like the new Control Center thing and the new sounds are neat. I haven't found anything I hate yet except that some of my calendar notifications are broken. So far so good.