The official Google blog entry offers a little more detail on each: The ability to talk back to customers is potentially handy when a review contains a feature request or implies a misunderstanding about how the product works.
The rich application snippets mean, in plain English, when a user searches Google for a certain functionality, a description of what the app actually does appears in search results, potentially driving interest. And the new category home pages are designed to highlight the most-installed and newest apps.
World-changing? Not really. But it's a nice set of enhancements for the many Google Apps partners augmenting their resale businesses with cloud app sales, in addition to the dedicated ISVs who are finding strong interest in the marketplace.