First up, they've introduced a new Explore section designed to enhance discovery. A new "Popular items" section helps the most interesting new stories bubble to the top. Popular items surface the news stories or viral videos gaining attention around the web, not just from within your own subscriptions.
The recommendations feature has been renamed "Recommended sources" and moved over into the new Explore section. It makes use of your web history if you're opted-in plus your Reader Trends to recommend new sources you might want to subscribe to.
The next change is a great step towards an even more personalized feed reading experience. The new personalized ranking feature re-orders the items in your unread feed based on your own past reading history and overall activity inside Reader. It gives you a view of your feeds informed by what you've liked and shared in the past.
To turn on the personalized ranking view, go to the Feed or Folder settings dropdown in the feed or folder you're viewing and select the playfully named "Sort by magic" setting. If you don't like the results, you can improve them over time by liking and sharing items in your feeds.