Google Play has long used so-called “carousels”, which display the icon, name and rating of individual applications, which you can see before you start scrolling the page.
In the design being tested, this feature switched to lists. Icons are a little smaller and Google now displays developer-provided ad text. By clicking on the arrow, you can go to view the full grid.
This visual change is at the top of the marketplace. It does not appear in the Games or Books tab. This change has not been widely adopted and is not present on all Google Accounts, according to 9to5google.