My laptop has needed a reinstall for a while now, so I decided to play a scorched earth tactic and try out the Windows 10 Insider Preview with the understanding that if it fucked up my Windows, I could just reinstall like I was going to.
I'd heard good things about the preview's stability, but my initial experience disagreed entirely. The final step of the installation was about as fragile as an empty egg shell, as I experienced the commonly reported issue of the installer freezing at the "Welcome back" step, and if you touch it it'll terminate and reboot only to freeze again. Indeed, the solution that worked for me was "leave it the fuck alone". This didn't inspire much confidence, but I pressed on.
Now, I realise that this is a technical preview, and indeed I installed it because I wanted to see how Mumble would react to it. I realise that there's likely to be a consumer preview to come yet which will have more of the UI fleshed out, but christ is the UI still half-done at the moment. It's definitely a step in the right direction from 8/8.1, but I think the correct approach would have been taking the good technical stuff from 8, backporting it to the 7 UI and going from there.
For instance, it's still (like 8 and 8.1) completely impossible to have a fully dark-theme (presumably without resorting to UI hacks anyway), and it looks like "Windows Classic" theme might be gone for good (not that I personally miss it, but I know people who will). I'm happy to report that the charms menu has been terminated with extreme prejudice, as has (unless I'm blind) most of the "magic corners" that frustrated new users of Windows 8 to no end.
Though there still seems to be no fucking way to refresh the list of available Wifi Access Points, among other confusing design decisions (I can understand and appreciate minimalism, but not to the extent of throwing away useful functionality). Also what I thought was a thinly-veiled attempt at getting me to beta-test "project spartan" appears to actually be a conscious decision to not let things like Chrome change the default URL handler - I'm not sure if that's a bug or a feature though.