It's barely been three years since Windows 7 ended Windows Vista's reign of error, but in those three years, computing has been upended by social media, touchscreen devices and app stores. Windows 8 is Microsoft's response to those changes, and much of it may annoy you if you don't understand that.

Windows 8 boots into a radically simplified Start screen (on the left in the composite image above) that displays apps and information as interactive tiles. That concept works well on Microsoft's Windows Phone 7 operating system and even on a laptop with only a keyboard and touchpad, it's still pleasant to navigate.

The Start screen's new apps — 9,000-plus of these one-click installs await in Microsoft's Windows Store — don't look like Windows programs either. Apps like Microsoft's Facebook-, LinkedIn- and Twitter-linked People don't have menus, and their toolbars are invisible unless you right-click on a blank area or swipe down from the top of a touchscreen.

To search or edit an app's settings, you have to tap or swipe in a right-hand corner to reveal an array of icons Microsoft calls "charms." You also need to invoke the charms list to get the time, check a laptop's battery or see the WiFi signal (which in my copy of Win 8, sometimes loses all Internet connectivity even as my desktop stays online).

With a mouse or touchpad, these gestures have you skating the cursor around the screen a lot. Even with a touchscreen, the new interface — the only one on the cut-down Windows RT edition intended for tablets like Microsoft's Surface – will take some learning.

That's not bad by itself. Having one app fill the screen, without distracting "chrome" above or below, brings the calming focus of a Kindle e-reader (though you can also "snap" an app into a left- or right-hand column to accompany another). The simplicity of navigation here also reminds me of Microsoft's Media Center and Apple's Front Row, alternate media-playback interfaces built for use without a mouse or keyboard.

But the traditional desktop, at right above, remains a click or a Windows-logo keystroke away. That preserves traditional Windows applications (except in Win 8 RT, which I'll cover in a separate post) and file folders (their windows now group commands in the "ribbon" toolbar Microsoft pioneered in Office 2007).

But there's no Start menu. So if you're on the desktop and want to launch a traditional Windows program, you'll often have to flip back to the Start screen, right-click and click an "All apps" button.

The cluttered Start menu desperately needed renovation years ago, but scrapping it instead of replacing it with a simpler apps menu (perhaps like OS X's Launchpad) seems crazy.

When I installed a preview release of Windows 8 alongside Win 7 on my 2011-vintage ThinkPad this spring, I was impressed by its speed and reduced memory consumption. But when I replaced 7 with 8 Friday morning — a tedious process that ground along over four hours — the never-too-fast laptop had become unusably slow.

I resorted to Win 8's new "Refresh" option, which keeps your files and settings, installs a clean copy of Windows and wipes out all third-party software that might have gummed up the system. Windows has needed this for years. And this time it worked, yielding a snappier machine.

So I don't feel bad about the $39.99 this cost me (a third of the $119.99 price of most Win 7 upgrades). But if your job doesn't require knowing new software, your computer lacks a touchscreen and you're content with Windows 7 — which should describe many readers — I can't think of why you'd want to pay even that low price right away.

Credit: Rob Pegoraro/Discovery