I installed the new iOS and iPadOS betas, and then proceeded to not notice much of anything to differentiate them from 16.6. The iMessage interface has a new menu for apps/photos/etc, and you can now long-tap on the iPad lockscreen to do essentially the same customization that iOS got last year. The new autocorrect seems fine, and you can say 'Siri' instead of 'Hey Siri'. Those seem to be the headlines?
There are two small enhancements that I do appreciate. The first is the new toggle to automatically delete text messages (and emails, if you use Apple Mail) with TOTP codes after they've been autofilled during a login flow. Super helpful. The other is more fine-grained app resizing on iPad when using stage manager. I use multiple windows on iPad every single day and it's a nice little thing to have.
The battery life hit that my iPhone 13 Mini has taken on this first developer beta is certainly higher than most years (I've done these beta shenanigans every year for about 10 years), but that's what you get when you blindly install experimental software not meant for daily driving.
The most exciting update for me is watchOS 10. The new ability to scroll the digital crown from your watchface and get a smart stack of widgets has been excellent. There are two specific things about this smart stack that I really like. If there's a timer running, it's now so much easier to see how much time is left (you previously had to hunt through the hexagon of apps, remember which of 3 orange clock icons is the countdown timer, and then tap it to load the timer). The other thing I've found very useful is your upcoming calendar events are shown sequentially as you scroll. Both of these things combined with the fact that I can keep my normal watchface and not commit to the 'Siri' watchface is the best of both worlds.
Also, the hexagon is dead, long live the hexagon! Your apps on watchOS 10 are still laid out in a roughly hexagonal shape, but instead of a free-flowing blob of icons, it's now a scrolling "list" that you can easily navigate with the crown. Nice.
I'm glad the watch is getting some love, otherwise I don't think most people should be clamouring for the iOS or iPadOS 17 betas. They feel mostly like a 16.7 release to me.