I just flashed the newest Dev Preview of Marshmallow, but I found the App Drawer looks different than most screenshots.
Is there a setting I need to set?
You're comparing the older Dev Preview 1 to the newer Dev Preview app drawer.
From an article on AndroidPit,
App drawer has been fixed
While we commend Google on trying a new, vertical-scrolling app drawer, the alphabetical dividers on the left and negative space at the end of some sections was a bad idea. The new Android M removes these and is faster to navigate because you have more app icons on screen. It still scrolls vertically though.
The old app drawer (left) and the new Android M developer preview 2 app drawer (right). / © ANDROIDPIT
AFAIK, there's no official way to revert back to the older version, unless you are OK with flashing Dev Preview 1 (and stuck with it).
Alternatively (though I haven't tried it, so do it at your own risk), based on another article on AndroidPit, try to replace Google App with older version, specifically the Android M Preview 1.
Install the new APK app for Android Marshmallow
Once you've installed Google Now Launcher (OP: already installed by default on Nexus), you need to download the Google App APK file. To do this:
- Make sure your device is set to accept downloads from unknown sources. To enable this, go to Settings > Security then tick the Unknown sources box.
- Next, download the Google App APK file to your device, which you can get directly by clicking here. Open the APK once you've downloaded it, then follow the instructions to install Google App.
Note: you probably need to uninstall Google App's update first. Also, by installing from unknown source, Google App can't receive automatic update from Play Store anymore.