Microsoft last night announced a technical preview of its upcoming Windows Phone 7 operating system -- the company's high-stakes attempt to come from behind against the likes of Apple's iPhone and Google's Android in the critical mobile market.

The timing is interesting, with Apple's iPhone 4 antenna problems possibly cracking open the door for more people to consider a new alternative. And along with the technical preview, several online reviewers have come out with their early thoughts on preliminary Windows Phone 7 devices they've been testing.

As a gauge of the company's progress, the reports are a mixed bag, with plenty of positive things to say (the user experience is feeling more solid, reports Engadget) but also some red flags, such as the continued lack of multitasking for third-party apps -- which means, for example, no playing Pandora in the background while doing other stuff on the phone.

Combined with no copy-paste function, Microsoft is at risk of putting out a "half-baked" Version 1 product, suggests Engadget chief Joshua Topolsky. Of course, the company has done that plenty of times before and ultimately been successful, in many cases, but in this situation it seems like a huge risk to take.

Other key aspects of Windows Phone 7 include its integration of the Zune music player and some basic Xbox Live features. Microsoft is betting big on the concept of "hubs" that will pull together common content (such as photos) from different apps into centralized repositories, making things more accessible.

Perhaps too accessible in some cases, based on the way Engadget reports its Windows Phone 7 "People" hub was flooded with Facebook contacts, making navigation a bear.

"Summing up, Microsoft’s doing the right things here with Windows Phone 7," writes analyst Michael Gartenberg in his hands-on summary. "It’s visibly differentiated from the competition but the challenge that comes with that will be explaining to the market why that difference is better than what we’ve seen before."

Also see this "definitive guide" to the Windows Phone 7 technical preview from ZDNet.

The first Windows Phone 7 devices are expected in October, and much will depend on how effectively Microsoft can rally the support of app developers between now and then. In addition to its recent developer tools beta release, the company will be courting mobile game developers at the Casual Connect conference in Seattle this week.

In the meantime, reading through the reviews of the technical preview, it seems like Windows Phone 7 will be a respectable first step in Microsoft's mobile comeback bid -- but at a time when the company really needs a huge leap to keep pace.