The most exciting feature of the whole redesign is one that I totally missed until I read about it in the mashable article, and that's the recommendations on the homepage. It surfaces some really interesting content, and plays on foursquare's strengths which are social data and time-sensitive check ins. Unfortunately, this feature is pretty buried at the moment, and is limited to showing generalized recommendations for the current time. There doesn't seem to be any way to dive deeper into the recommendations by time/date, or to filter by category. There's a lot of potential there however, so I'm excited to see where that goes.
It is also really surprising to me that foursquare does't have a map on their search page if they're pushing local discovery.