The new interface does away with rounded corners look and sports squared corners. The rounded corners, drop shadows and colored backgrounds of sidebar navigation were quite distracting which have been removed to give a minimalist cleaner look.
Below are screen-shots of both old and new look of Google Reader.
The sidebar navigation now contains collapsible panels so that you can hide them when not required. Also, you can hide unread items count from feed list as they may cause anxiety in case large number of items are unread. Now friend’s shared items are placed in their own panel in sidebar.
The dirty Add a Subscription link with green background has now been given a decent look and placed on top of sidebar.
Another major change in Google Reader is the feed bundles, which used to be created manually by Google Reader Team and now they are automated. Just click on Browse for stuff in sidebar to get recommended feed bundles based on your reading habits.