Windows 10 [official site] looks like one of the good versions of Windows, one you'll upgrade then stick with for years as Microsoft add guff to later versions that you couldn't possibly want - joining the likes of Windows 98 SE, 2000, XP, and 7. It seems to mostly do good things, promising faster boot times and the return of the Start menu, and at worst things I'm different to, like Siri-esque voice-controlled computer friend Cortana and some Xbox One guff. And it'll be free to upgrade to from Windows 7 or 8.1.
This morning Microsoft announced Windows 10's release date: July 29th.
On the games side of things, the launch of Windows 10 will bring the launch of DirectX 12, which looks like it'll be able to boost game performance by reducing driver overhead. It'll bring a touch of Xbox integration, though that sounds far less awful than ye olde Games for Windows - Live. It'll bring support for cross-platform play between PC and Xbox One versions of games, like the free-to-play Fable Legends. Folks will also be able to message Xbox chums and all that.
You might have noticed your PC pop up a little notification that you can now "reserve" a free upgrade to Windows 10. If you go ahead with that, your PC will automatically download Windows 10 when it's available then prompt you to install it when you please. If you're forgetful, sure, that's helpful. I am forgetful, and have signed up. You'll still be able to upgrade for free for a whole year after launch if you don't want to "reserve", of course.
Windows 10 does more than I've said, of course, but I can hardly reel off every feature of a new operating system. Here's a video showing some of that: