Certain options are missing from the left side of this Start menu, but it's a faithful recreation of the menu in Microsoft's latest (and probably greatest) OS. This does raise a couple of intriguing points, though.
When Windows 8 came out, many said that the full-screen Start screen was attempting to make a desktop OS feel like a mobile one - a point that's hard to disagree with on account of the fact that Microsoft implemented many gesture features around it. Now, we're seeing the opposite thing happen - Microsoft is releasing a Start menu for a mobile device that's better-suited for the desktop. Perhaps this is proof that Microsoft actually regrets the full-screen Start menu and is glad to purge it away.
Nonetheless, if you have a Windows RT device, you'll be able to snag the update through Windows Update. It's unclear at this point if the Start menu is the only new feature added in this update.