Android 6.0 Marshmallow is known for its new Doze battery smart feature, which can save hours of battery life on the phone. This is by putting your phone into ultra-low-power state when it is not being used. Android 5 Lollipop and above users can now get the Doze battery smart feature with a standalone app called Doze.
An unofficial build of Android 6.0 Marshmallow update is now available for the Nexus S. Currently running on the Android 4.1.2 Jelly (last updated in Oct 2012), the old hardware on Nexus S (1GHz CPU, 512MB RAM &16GB Memory) is just about capable of running the new Android 6.0 Marshmallow. Interested tech-savvy users can update their Nexus S to Android 6.0 Marshmallow with the unofficial AOSP based ROM
Released in November 2015, the mid-range OnePlus X has great specs and features, but if you are an Android fanatic who want to run certain apps that requires root access, install custom ROMs, backup/restore the system, etc. need unlocked bootloader, root access and a custom recovery on it, though it involves certain risks.
Google Now on Tap is the headline function of Android 6.0 Marshmallow. The all-new contextual assistance is pretty smart and can give information for almost anything on your screen, even before you ask the question. Instead of just using keywords, ‘Now on Tap’ will tailor search based on its context and give you an accurate and fast result.
Nexus devices running on the Android 6.0 Marshmallow can now root without modifying the system partition, which makes it easier to apply the OTA update. Though, currently an experimental feature, Chainfire’s latest SuperSU (SuperSU 2.56 Beta) can give root access on Nexus 5/5X, Nexus 6/6P, Nexus 9 & Nexus 7 2013 running on Android 6.0 without modifying the system partition.
The good old Nexus 4 will not get official Android 6.0 Marshmallow update from Google, though the device is capable of receiving the same. However, developers are busy working for a fully functional near stock Android 6.0 Marshmallow custom ROM for Nexus 4. An XDA developer ganachoco has released a near stock custom ROM based on the Marshmallow for Nexus 4 that you can flash via custom recovery.