I generally like new Android releases, but for me this one's a huge miss. While I like the new look and feel (I use Nova launcher, so changes are minimal), there are a couple of things for me that would have made this a deal-breaker on a new phone.
The main one is that they've broken location services by removing the battery saver mode. Right after the upgrade, I had at least twice the battery drain. I was down to 50% by 10am, which is normally where I was at by 6pm (coming off a 5:30am charge). When I turned location off, the battery life improved, but now any widgets (like weather) are disabled due to lack of location. And it's not just a matter of turning it back on to refresh the weather. If you do that it takes quite a while for the widget to realize it knows where it is again.
My other problem is not being able to hide the taskbar clock. I've gone in to System UI Tuner to hide it, but that doesn't work anymore. It pretends it's hiding it, but it's still there. Clear all apps from the tasks screen is now hidden all the way to the left, and if you have a light wallpaper you're going to miss seeing it. Give it a blurred background or something to make it more obvious.
That said, it does seem pretty smooth, and I do like that dark mode is back for some items.