According to scribbal, new features include a panorama dashboard view of the updated Places, Friends, Me, and Explore screens, as well as a Leaderboard Live Tile, and sort options for places by “here now” and friends by name.
From a post on the foursquare Blog:
We want anyone, anywhere, on any platform, to be able to check in with foursquare. When Microsoft unveiled Windows Phone 7, they wanted to make sure foursquare was available with their awesome new OS, and worked with us to build it. Today, we’re super excited to announce a total rebuild of the app, with a ton of new features.
We collaborated with Microsoft to develop the app entirely on our open API v2. The new version really speaks to the distinctive capabilities (and slick design!) of Windows Phone, while maintaining the foursquare features you know and love. Playing around with it, what’s cool is that it feels both familiar and new, with a personalized experience through the lens of Windows Phone 7′s panoramic UI.