After nearly two years of waiting, Windows Phone 7 is now a reality.  The first handsets powered by the new mobile OS won’t be available for purchase until early next month, but some reviewers have gotten their hands on final hardware and the first round of reviews has begun. 

Here’s a brief summary:

Walt Mossberg: WP7 is innovative, but not particularly compelling for most users.  Mr. Mossberg is concerned about the relatively small library of apps, lack of basic features like copy-and-paste and tethering, but thinks things will improve over time.  [Full Review]

Engadget / Joshua Topolsky: Fast and responsive, Windows Phone 7 offers a beautiful and usable UI.  Great soft keyboard.  Built-in Office support “one of the biggest differentiators” of WP7. “[T]here’s a lot to like or even love in WP7,” but it’s “not there yet.”  [Full Review]

Paul Thurrott: Without question the most glowing review, Mr. Thurrott (who has written a book on Windows Phone 7) believes the new OS is a “game changer” that will help set the course for future smartphones.  While not perfect, the OS is highly usable and useful and will be tweaked and improved over time.  [Full Review]

Ars Technica / Peter Bright: Metro UI is “brave.”  What WP7 does it does well, but there are a lot of things it just doesn’t do.  In the final analysis, Windows Phone 7 is a good first step and “a winner.”  [Full Review]