The Foursquare app on Windows Phone has always been an interesting one to watch, as it has had a lot of support from Microsoft and Nokia in terms of resources and development time. Windows Phone 8 users picked up the new UI in the summer, and this update also brings it to Windows Phone 7 users, unifying the user experience across the Windows Phone platform.
Thanks to the increased focus on discovering new places, the Foursquare app can be used without logging in to find interesting locations and venues near to you. While this dilutes Foursquare's original mission (to have the check-in drive a gaming experience), it represents the space that Foursquare is now looking to fill, namely guiding you to interesting things around you, an area which should have greater revenue generating potential for the location based web service.
The app still falls slightly short of the feature set that is available on other mobile platforms, such as checking in to events or checking in with friends - but there are indications that these will be available in a future update.
For now you can download the Foursquare client for free via the AAWP App Directory.