“I think it’s functional, clean,” said Andries van Dam, a pioneer in computer graphics and a Brown University computer science professor, who receives research money from Microsoft. “I welcome it.”

Younger users may be more likely to embrace the new approach. Joanna Lin, 23, who works in sales and marketing for a hotel chain in New York, said she was impressed with the software. “The feeling was very fluid,” said Ms. Lin, who was the most enthusiastic of five people that The New York Times asked to briefly try Windows 8 last week. “Definitely a step up from Windows 7.”

But the product is a major gamble for Microsoft, a company whose clout in the technology industry has been waning. The PC business, which generates much of Microsoft’s revenue, is in a severe slump as newer products like smartphones and tablets take more dollars from peoples’ wallets.

To help it gain traction in the mobile market, Microsoft made Windows 8 a one-size-fits-all operating system for touch-screen tablets, conventional computers with keyboards and mice, and newer devices that combine elements of both. (Confusingly, Microsoft is also introducing a separate but similar operating system, Windows RT, that cannot run older programs.)

Apple took the opposite approach with the Mac and mobile devices like the iPad, which have distinct interfaces, albeit with some shared technologies. Timothy D. Cook, Apple’s chief executive, has said of Microsoft’s strategy: “You can converge a toaster and refrigerator, but these things are probably not going to be pleasing to the user.”

Jakob Nielsen, a user interface expert at the Nielsen Norman Group, conducted tests with four people who used a traditional computer running Windows 8 and found that they had “a lot of struggles” with the new design. Mr. Nielsen said they appeared to become especially confused when shifting back and forth between the modern Windows 8 mode and the desktop mode.

Mr. Nielsen said Windows 8 was more suitable for tablet computers with their smaller displays, but it was not helpful for workers who needed to have lots of applications visible at once.