I upgraded two iMacs and a MacBook Air to macOS Big Sur. One of the iMacs was not happy after upgrade but booting into rescue mode and reinstalling Big Sur fixed whatever was ailing it. My initial impression is positive. I like the UI changes and the updates to core applications. Performance seems a little slower but gets faster after apps have been used a couple times. Might be some data migrations happening in the background? Bringing Widgets and Control Center to macOS seems like a win. I have a lot fewer menu bar icons.