Both Engadget and Mobile Burn have been given previews of the next version of Windows Phone 7, installed on real world hardware. Mango will be the variant of Windows Phone that will power Nokia's first handsets in partnership with Microsoft. There's been a lot of people pointing out missing features and wondering what the OS would look like at the end of 2011, and with the caveats that these are still developer builds, these previews should help a lot.

So what's the opinion on 7.5?

Engadget:

Wonder of wonders, miracle of miracles, Windows Phone is developing into the OS we've been asking for since we first used it last year. By adding in crucial elements like multitasking, groups, social network integration and more, it's starting to play catch-up to the other big names in mobile. Not overcome -- catch-up. Mango hasn't shown us anything truly groundbreaking yet. At least this platform, still in its youth, is stepping onto the same playing field as hard hitters like iOS and Android, though. One thing that surprised us was how few bugs or choppy effects were present in this build, an impressive feat considering we're still a few months away from completion. Overall, we've come away with a positive outlook on Windows Phone's newest iteration, and are very eager to see the finished result.

Mobile Burn:

...I feel that the changes Microsoft has put into Mango go a long way towards filling any gaps that existed in the initial release of Windows Phone 7. The best part is that while Mango catches up with the other major smartphone operating systems, it still manages to remain true to itself. It's different, to be sure, but Microsoft's OS is beautiful, fast, and powerful as well.