On the security side, Settings now puts Security front and center. Additionally, Oreo brings tighter app install controls, and has Google Play Protect built-in. To alleviate charge concerns, Android Oreo minimizes unintentional overuse of battery from apps in the background.
Picture-in-Picture is a useful new addition that allows you to see two apps at once, so you can, for example, check your schedule while being on a video call without having to swap apps. Notification dots let you tap to see what's new in your apps, meaning you can view notifications only for priority apps.
Oreo also features built-in support for Android Instant Apps, letting you check out new apps without having to install them, and also features a team of fully-redesigned emojis.