As Google Officially announced their latest OS called Android M or Marshmallow(Android 6.0) on 29th September with
Nexus 5X and Nexus 6P being the first to have it pre-installed though it will be rolled out to other nexus device first.
I know some of us can't wait to have the Android 6.0 installed in their phone, so check out the features its got before you have it installed on your phone.

Android M(Marshmallow) 6.0 features

A new App search bar design:

There will be a search bar added to the application menu which will help to access your favorite app easily by typing the name of the app. Some launchers have this feature but with Android 6.0 Marshmallow you won't require any launcher to enjoy this feature.

Having full control over app permission:

App permissions will also change in Android M. Rather than requesting your permission to use certain features at installation time, Android M apps will request permission for activities the first time it is required.
Permissions have also been simplified, and will now be requested the first time you try to use a feature, not at the point of installation.

Support for fingerprint scanner:

Fingerprint scanner in Android smartphone always come pre-installed in a device by the manufacturer but with the Android 6.0 Marshmallow, fingerprint scanner will now be supported on any android device that has the Marshmallow installed. With this feature you can be locking your phone with your fingerprint, not only with numbered password or drawing on your screen.

USB Type-C/3.1 support:

With the new update it now fully support for USB-C, which is closely linked to the USB 3.1 standard. We’ve seen this plug already in the OnePlus 2, but it was really just a USB 2.0 port with a different connector.

The big news is the new set of capabilities we’ll see when ‘proper’ USB-C phones arrive, with USB 3.1 support. They’ll be able transmit 40x the power of the current USB connectors.
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Auto app data backup:

The Android 6.0 Marshmallow creates a copy of practically everything an app needs to be reinstalled and pick up where it left off. All the data is backed up to Google Drive, from which it can be plucked and placed on a new or reset device. So all your data, settings and passwords go back to how they were as if nothing ever happened.

A new RAM manager:

Google has introduced a new RAM manager to Android M, with the aim of providing users with more accurate and comprehensible information regarding the maximum and average RAM usage of apps.

With a reading of an individual app's RAM consumption, as well as how often it is running in the background, users will be able to better determine which apps should be removed in endless bid to increase device performance and battery life.

Rotation your screen when it's on home screen
This is another feature that haven't been on any android smartphone, with the Android 6.0 Marshmallow installed on your phone you can rotate your phone when it's one home screen. We know in all Android Smartphones you can't rotate your home screen apart when you are on app menu or using any application but with Marshmallow you can achieve that.

New file manager design:

Internal storage is always a problem for most mossmartphone users. Even with microSD expansion and USB On The Go (OTG) you always seem to need to keep an eye on available storage space. The new version of Android M introduces a simple line bar that shows how much space you have on your device with a breakdown of what is using up your internal storage.

Battery improvement:

Many people complained about the Android lollipop killing them battery, some even claim they prefer jelly bean to lollipop but with Android 6.0 Marshmallow you won't experience the battery drainage problem you were experiencing with lol. It will optimize your phone's battery through power saving.

http://www.zpykios.com/2015/10/android-marshmallow-features-should-know.html?m=1

Zpykios

Your explanation on the fingerprint scanner is wrong. Android Marshmallow does not miraculously put a fingerprint scanner on your device. It only supports the fingerprint sensor that comes with your device by making it possible for you to authenticate app purchases with your fingerprint or secure your phone. Without a fingerprint sensor installed on your device by your device manufacturer, you cannot take advantage of this Marshmallow feature.