Back when Android L was announced as a Developer Preview during Google's 2014, we were all blown away with the more realistic and colorful direction that Material Design was taking. When the preview got onto devices however, people soon realized that staple features that people had relied upon for years had either been removed entirely or drastically changed. The Developer Preview of Lollipop completely lacked a "clear all" notifications button, which was thankfully re-added in the final build. For some though, the volume controls and notification sound control continue to be a problem for users. Android M hopes to fix all that.
During Google I/O 2015, Android M was one of the bigger announcements, but many of the features were simply skimmed over, like the new text selection and quicker sharing features. Another of those features - which got considerable applause from the audience - was a change to the volume controls in Android M. Now much easier to work with, touching the volume rocker on your device will of course raise or lower the volume, but there's a neat little arrow on the right that allows you to expand the controls. This allows you to once again, quickly control different volume levels as in previous versions of Android. This feature works the same on either Android tablets or smartphones running Android M, and this is one Android M feature we can't see Google changing too much before release.
The Android M Developer Preview is available to anyone that wishes to try it out on a Nexus 5 or above, however you shouldn't try it out unless you're willing to deal with some bugs here and there as well as a somewhat limited experience. Still, it's nice to try out the new Android before it's released in earnest later this year. We've already covered some other changes to Android M which appear to be a return to the older ways of doing things in Android, like the vertical app drawer, as oppose to the horizontal one introduced quite some time ago.