Google has without any change log or notification changed the app drawer of its Google Now Launcher from the horizontal paginated list that we have all grown accustomed to a vertically scrolling one, as found in the Android 6.0 Developer Preview.
Google pushed this update through its Google app, which essentially contains all the code for the Now Launcher, and not through the Google Now Launcher app. The vertical scrolling app drawer and quick search functionality are better in terms of usability, but might not be liked by everyone.
Since Google is not providing any way to switch back to the previous horizontal app drawer, your only option is to switch to Nova or Action Launcher if you are not fond of the vertical app drawer. Even better, Google does not mention anything about this change in the change log of the app update for its Google app, so most Google Now launcher users are going to be surprised when they open their app drawer next.
What do you think about this new vertical app drawer? I like it better than the horizontal one because it makes it easier and faster to find the app you want to open. Plus, the list of frequently used apps at the top is very useful.