Using this on my daily driver 16 PM, other than a stuttering UI which a reboot doesn't fix, mainly the home screen, iOS 26 is working very well for a first beta.
I like what they are trying to do with liquid glass, but it needs to be toned down a bit. Apple has a lot of work to do on it by the time it's released.
Biggest improvement for me is wireless carplay on iOS 26 now works so much better and more reliably on my aftermarket pioneer head unit even on beta 1. On iOS 17 it was rock solid, never had a single disconnect, on 18 it's been a complete disaster. May connect and stay connected ok, but other times it would connect and then rapidly disconnect and reconnect in a second or two, could do that two to four times once the car was started and then it would be absolutely fine until the car is restarted.
So far it's been perfect, as they've been working on CarPlay for this release, they've finally fixed whatever was causing my issues. It would have only taken them a year to fix it by September.