Various parts of the Google app are seeing some Material Design 2 changes being implemented to the UI. One of the more noticeable visual adjustments that Google has made is with the Feed, which will be the first thing you see when you open up the app. Right now the Feed in the Google app shows the cards for different things layered on top of a white background. In the new Material Design 2 changes the cards are still there but the white background is no longer present and Google instead seems to have switched things to a sort of frosted glass look by using a blur effect on background images, which you can see in the screenshots below.
This change should help the cards stand out more. It's also worth noting that the MD2 visual tweaks are reportedly in testing at the moment so the majority of users who access the Google app likely won't be seeing the changes just yet. In addition to the new blurred background image for the feed, the feed is also sporting the new look for the Google search bar. While some users will see this in the feed again after it disappeared for a bit, the new look changes things up by extending the Search bar from nearly edge to edge with rounded corners, and takes away the layered shadow effect that currently sits behind it. This bar will be sitting just below the "Google" branding.
Other changes that seem to be on the way are a customize widget shortcut that you can find sitting in the "More" tab which will be the right-most tab in the nav bar down at the bottom of the app's UI. As the name of the shortcut suggests this will let you customize the Google widget that you'd place on the home screen, if you have any desire to customize it in the first place. You'll also find two new options in the Assistant settings, which are Stocks, and Reservations.