An inevitable change is coming ever since Google revealed its new Material Design aesthetic at Google I/O 2014 last month. Although the rest of Android 4.4 will remain stuck with the Holo-based design, Google has begun to eat its own dogfood and applied its new design principles on its own apps, starting with Google Play Store.
The changes in the latest 4.9.13 version of Google Play Store isn't exactly earth shattering and is, in fact, quite incomplete. Google seems to be implementing visual changes piecemeal and in this round has focused on applying it to individual app pages before using it on the entire app interface. That said, the changes are immediately visible and not so subtle and you will quickly see the focus on graphics, flat icons, and paper metaphors that are the hallmarks of Material Design.
Almost immediately, when you tap on an app, you will be greeted by an app's banner or video, if it has either one. If not, the usual icon and app name will be at the top. Although each app page is still separated into sections, they are no longer as delineated as in the previous Google Play Store version. You could say that, at least for the main content, they all reside in the same sheet of paper, separated only by thin lines. Individual reviews, in fact, don't even have line separators and just flow together as a whole. New to this layout is a row of buttons, of course in Material Design fashion, that are shortcuts to various sections like ratings, app category (Tools, News, etc.), Google+ contacts who +1'ed the same app, and Similar apps. Unfortunately, you won't see any of the paper-like animations and depth levels detailed in Material Design, since that would most likely require Android L's theme engine.
As always, updates to Google apps happen in staggered waves but, unlike common apps, you don't have to do anything to get this update. However, you can always query the server to check if an update is available, by tapping on the Build Version in Settings, or, if you really want it now, you can download the Google Play Store 4.9.13 APK from the link below.