Below is a list of officially stated changes as well as some others I've found. I'll update this list as I explore the O.S more.
* Google's final AOSP has been implemented.
* Overscrolling effect has been changed from glow to stretch (similar to iPhone if you've ever tried scrolling up or down a screen)
* Reliability of voice commands in Camera has been improved
* Pet Lighting Effect (?)
* Color Theme Function Stabilization
* Keyboard text shortcuts have been fixed
* Call and text on other devices crashing on startup is fixed
* Bixby on lockscreen has been fixed
* System UI crashes have been fixed (likely the soft restarts, I hope!)
* Weather app redesign
* Dark mode icons no longer "flicker" upon returning home (they stay the same shade).
* Some widgets now have a smoother transition when entering / exiting them
* Performance improvements
* [Accessibility Option]
Reduce transparency and blur effects fixes
* [Beta 2 but worth pointing out] Extra Dim's intensity can be adjusted. Can be disabled after restart if you enable that feature.
* App Splash Screens have been fixed
* Task Switcher Animations have been fixed (my constant complaining worked for once)
* More under the hood improvements
Please list any problems or new features you find! Hopefully we'll only need 2 or three more beta builds before a final release.