So I just installed the M Preview and got a few screenshots of new/different things I've noticed.
Initial set up screens are slightly different from Lollipop. App drawer now scrolls vertically with the four most recent apps at the top. The quick settings tiles are slightly different. There's a new "Do Not Disturb Access" menu option along with another option to access all your Google settings directly from system settings. I'm not sure if the "inactive apps" option as well as the option to have light, auto or dark system themes existed in Lollipop but if they didn't hear they are!
I'll run this for a few days and let you know how it goes.
Update 1: Looks like we can now disable heads-up notifications on a per-app basis by going through the app info screen
Initial set up screens are slightly different from Lollipop. App drawer now scrolls vertically with the four most recent apps at the top. The quick settings tiles are slightly different. There's a new "Do Not Disturb Access" menu option along with another option to access all your Google settings directly from system settings. I'm not sure if the "inactive apps" option as well as the option to have light, auto or dark system themes existed in Lollipop but if they didn't hear they are!
I'll run this for a few days and let you know how it goes.
Update 1: Looks like we can now disable heads-up notifications on a per-app basis by going through the app info screen