It has been a couple of days since the update rolled out to Indian variants of the Galaxy Note 9. Overall, performance has improved quite a bit (compared to the March version). Stutters have reduced a lot, haptics have improved and, most importantly, at least 6 apps stay in memory for a longer period of time (it used to be 2 or 3 before). For those experiencing stutters and lags, I would suggest trying to wipe the cache partition before looking into the option of formatting.
With respect to battery, I urge you all to explore the option of Deep Sleeping apps. For the first time in a while, I got close to 4 hours of SOT over 30 hours with max resolution (my phone is 1.5+ years old), Bluetooth always on and connected to my Galaxy Watch and WiFi always on. I also live in an area with very inconsistent network signal.
However, I did find a few features missing in this update.
No dark mode on Galaxy Store (I don't want to use HEX installer).
No auto-grouping feature in the Gallery even though smart crop is available and working fine.
No night hyperlapse and super-steady modes in the camera (Samsung didn't commit to these anyway).
No smart selfie mode as well (again, no commitment from Samsung).
Messages - I don't understand the point of having an "All" section when I am anyway putting conversations under different groups. It doesn't make sense to me. And, no RCS in Samsung Messages.
I'll add to these if I come across others. Please let me and everyone else know your take on the update.