I recently upgraded my 2013 Nexus 7 to Marshmallow with an over-the-air (OTA) upgrade. While Google has no plans for a Nexus 7 2012 OTA upgrade, you can, contrary to most accounts, manually update the 2012 model to Android 6 (a.k.a. Marshmallow) using the nakasi and nakasig builds.
At first glance, there's not a lot of difference between Lollipop, Android 5.x, and Marshmallow. The new interface has the new Google branded look, but that's about it.
However, the differences soon show up once you start using the new Android.
The most interesting change, so far, is Google Now on Tap. With this feature, Android displays pertinent information based on the information your app is currently showing on the screen.
You can use Google Now on Tap in two ways. If you hold down the home button, Marshmallow shows what Google believes to be helpful apps and information about the page. So, for example, in the screenshot above, Marshmallow displays social sites about the movie theater I'm looking at, a movie showing at that theater, and Meryl Streep, who's acting in one of those movies.
The second way to use Google Now on Tap is with OK Google voice search. Using this, I can ask for restaurants, and Marshmallow shows me places to eat that are close to the theater. This makes it the perfect "dinner and a movie" app (though all my friends know I'll only order a hamburger no matter where I go).
Or rather, Google Now on Tap would be a great feature, if it worked reliably. At this point, some of its answers aren't to the point. As Google gets a better handle on how people are using this new functionality, I expect this app to improve quickly, as with ordinary OK Google and Apple's Siri.
This function is turned off by default. But, unless you're paranoid about your privacy, it's well worth turning on.
Speaking of privacy, Marshmallow makes it much easier to manage permissions. In the past, when you installed or updated a program, you were shown a mess of permissions: a list of applications and OS features that the new application wants permission to access. Most of us tend to just hit OK rather than deal with them, as we do with end-user license agreements (EULAs).
The new Android version enables you to easily access each apps' specific permissions by way of Settings/Apps. Find the app you want to fine tune; then, go to permissions and set the permissions the way you prefer. For example, I have no idea why Amazon Kindle wants permission to access my contacts and phone. But now, by turning those permissions off, I've made sure it can't call a friend at 2AM to sell her a book.
One old feature is back and better than ever: Search in the app drawer. If you have hundreds of apps, it can be darned handy to type in a few letters and get to the app you want right now. Google also puts your favorite (most-often used) apps at the top of the search drawer. I can live without search, but I really appreciate the latter feature.
You'll also notice a much quieter feature, Doze, after you're done playing with Marshmallow. When you pick up your smartphone or tablet again, Doze may give the device more battery life than it usually would after sitting idle.
That's because when your device is unplugged, still, and its screen is turned off, Marshmallow goes into Doze mode. It's not a restful sleep. The OS still wakes up, every now and again, to sync apps and to pull in notifications. It also works out which apps you don't use often and keeps them quieter still. The net result seems to be a battery life improvement of approximately 50 percent.
There are also smaller, useful updates. For example, when you try to select text, Marshmallow defaults to selecting whole words. For klutzes like me, this is really useful.
The volume controls, which went a bit haywire, in Lollipop, are once more easy to use. Thank goodness!
Less useful, in fact a bit weird, is that you can use an external SD card as "internal" memory. I say "weird," because that external SD storage doesn't simply add to your internal storage, it replaces it. So, if you have only a small amount of internal memory -- 8 to 16GBs -- this could be worth doing. If you have more, say 64GB to 128GB, it's probably not worth your time.
Does Marshmallow sound good to you? Want to check it out for yourself? You can manually check to see if an over-the-air Marshmallow update is available for your phone or tablet by going to Settings->About device->System Updates>Check for Update.
If that doesn't work, you can install the new OS by downloading the Marshmallow factory image for Nexus devices to your PC. Once the download is complete, go to the "platform tools" folder and extract the factory image. Then, boot your device in Fastboot Mode, connect it to the PC using a USB cable, and run the flash-all.bat script. But before you jump into this, note that this process erases all your installed apps and data.
As for me, if you'll excuse me, I have some more Nexus devices to upgrade to Marshmallow. This is one upgrade I'm eager to install on all my Android gadgets.