The launch was seen critical for the company, particularly after the poor response to Windows 8, an ambitious redesign that confused many users by ditching the start button menu and introducing a new layout.
The new OS, launched on Wednesday, will be available as a free upgrade for users of Windows 7, Windows 8.1 and Windows Phone 8.1.
Wall Street Journal's Geoffrey Fowler said Windows 10 fixes most of the issues with Windows 8 and improves on Windows 7, Microsoft's most popular OS in recent years.
For one, the start button is back.
"Three months of testing Windows 10 determined that this familiar yet fresh overhaul far outweighs any problems," Fowler wrote in his review.
By offering free upgrades, Microsoft aims to put the system on as many devices as possible. The company would then make up for any lost revenue by selling services such as Office over the Internet, or cloud.
FBR Capital Markets analyst Daniel Ives said the cloud strategy could generate a new revenue stream.
"It's a step in the right direction. They went back to their core DNA around software and a cloud-centric model and ultimately Windows as a service, a subscription model," Ives told Reuters.
Microsoft, which unveiled Windows 10 in September, skipped Windows 9 altogether, to put some distance between the new system and Windows 8.
At least one prominent reviewer was skeptical, saying the new OS was unlikely to boost PC sales or salvage Microsoft's Windows phone business.
Re/code's Walt Mossberg said some features were promising but the new OS was "surprisingly buggy".
"I doubt it will convert many Mac owners, spur a shopping spree in new PCs, bring in droves of new developers, or save the Windows Phone," Mossberg wrote.
Almost all critics lauded the return of the Start button.
"I can't start a review of Windows 10 without heralding the return of the Start menu," USA Today's Edward Baig wrote.
"The newly revamped Start menu in Windows 10 is a useful combination of Windows past and present and a metaphor for the entire direction of Windows 10," .
Windows 10 also comes equipped with 'Cortana', a digital assistant similar to Apple Inc's Siri and Google Inc's Now.
© Thomson Reuters 2015
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