It finished installing!
On first boot, it took a looooong time to do the initial setup stuff. It said something like "Hi. Please wait while we set up your apps & settings." then after a while it said "Just a few tweaks left." then after a while longer it said "Unfortunately, this is taking longer than usual." That message displayed for a looooong time. Just when I was almost certain it was stuck, it showed the desktop!
When I finally got to the desktop, I was greeted by a critical error. "Oops, something is wrong with Windows installation. We'll try to fix it the next time you sign in. If signing out and back in doesn't help, you may need to reinstall Windows." Thankfully, signing out and back in seemed to fix it.
I haven't had to sign in with my Microsoft account. I guess that's due to it being an upgrade from an existing Windows 7 installation. The default color scheme for the taskbar is poor. The task bar is dark, and the font color of text is black, so it's very difficult to read. I'm not sure if that's default for the preview or if it's a problem due to upgrading from Windows 7. I tried Right Click -> Personalize and it opened a Settings window, but then before anything actually showed up in the window I got a BSOD.
After a reboot, the settings window seems to work now. Well, sort of. I opened it up and played around with a few things. I got it to change the color of the taskbar based on my background (which somehow changed from some tulips to a blank blue screen since my last reboot). That's kind of cool. Especially if you have your backgrounds/wallpapers on a slideshow to change every so often. After changing that, I was looking at other settings when the window just randomly closed.
It seems pretty unstable, but I guess that's to be expected in a preview build. Every native Windows 10 app seems to crash/close randomly the first couple of times I run it before I can do anything with it. But I've probably explored Windows 10 more in just the past hour or so on my netbook than I have in my VM over the past several months. I discovered (or re-discovered?) that Windows 10 supports multiple desktops natively. That's cool.
Other than things closing/crashing randomly, it seems to run as good or better than Windows 7 did. (Which wasn't very good on this decrepit machine.) But I really haven't done anything to push its limits yet, and it's not an objective observation and could be wrong.
I've been playing around and experimenting somewhat as I type this, and I just found the old Windows Vista/7 style theme customization window, and I selected the default Windows Technical Preview theme and the colors are better, so I guess it was just a bad theme upgrade.
I like the new task manager. It seems to have more useful/detailed information.
I'm thinking I'll like Windows 10 once it's stable.