WPCentral posted a review on the preview release of Windows Phone Mango

To say "Mango" for Windows Phone 7 is a large update is a bit of an understatement. It's massive. Although we have had two updates to our fledgling OS, both have been relatively minor. "Mango", however, is Microsoft's attempt to fill in all the gaps left from the v1.0 release last fall. Can it succeed?
We've been able to handle a preview release of "Mango" for the last few days and have put it through various tests, comparisons and the all important "just using it like a normal phone". Our device was the venerable Samsung Focus running Windows Phone 7.661.WP7_5_Trial (mojobld).20110607-1957, which means this is a relatively late build (June 7th) and as you can see, Microsoft seems to be going with "7.5" for this release.

  Windows Phone Mango (preview release) Review