I have a 3 year old HP laptop. Fully patched / licensed Windows 10, 12GB RAM, Intel i5-8250U CPU @ 1.80 GHz. Upgraded last year to a TB SSD drive. Sitting around yesterday and saw that the Windows 11 update was available, so though 'why not?'
I had already downloaded and run the PC Health Check, which tells you if your system meets the Windows 11 system requirements - my system passed. Went to the Download Windows 11 website and chose the Download Now option - this option allows you to upgrade your system in place. There is also the option of downloading an ISO image to do a clean install. I had a complete backup, so decided to update in place.
The only issue I had during the install was that I forgot that my login account does not have full admin permissions and so the install failed a couple of times. When I figured what was happening, I located the Windows 11 Installation Assistant file that is downloaded at the beginning of the process, right-clicked on it, selected Run as Administrator, and all was well.
The update took about an hour with a couple of restarts. When it had finished, I logged into Windows 11 without any drama at all. All files, folders, and programs are where I left them. The taskbar looks different, with the icons centered (I right-clicked on the taskbar, opened Taskbar Settings, selected Taskbar alignment and selected Left - looks more normal to me).
Today, I ran Windows Update, installed a couple of updates and some driver updates; all installed fine. System runs great, seems a bit faster than Windows 10, but may be me with something 'bright shiny'.
So initial thoughts are that Microsoft nailed it, producing an update was essentially flawless.
Will follow up if anything odd happens.