Android 5.1 vs Android 6: Google Photos
Google+ Photos isn't technically new to Android M, but it replaced the "Gallery" app in Android 5.1, and is now just called Google Photos, and is more powerful than ever.
You have unlimited Google Photos cloud storage, so you'll never lose a photo even if you lose a device. It automatically makes GIF, movies, slideshows, or vacation presentations with photos to share with friends and family, and backs them all up automatically too. Everything is separated by event, location or date, and a pinch will widen the view so you can see more (or less) photos at once. It's similar to Apple's photo app, but that's a good thing. Google Photos is an extremely powerful app we recommend everyone try today, so get it on the Google Play Store. Make sure you head into settings and set backup on WiFi only to save data, and to use High Quality backups for unlimited storage. Otherwise you'll have a limit, and can fill it after a year or so.