Battery life is greatly improved for me (25% longer lasting so far) but auto-brightness does seem to be quite a bit more aggressive. Phone feels much snappier, too. Camera responses, especially when zooming/toggling between lenses seems improved.
This could be an AT&T app I haven't disabled or something else completely, but since the update I no longer receive any notifications when my phone is connected to my car's bluetooth. I get what looks like enhanced Android Auto experience (again, could be just update to AA app) when using Native Android Auto in my Civic. Notifications [I do get these when phone is plugged into car/AA is active] and navigation in general are much snappier and appear in a more crisp and desirable manner.
The only issue I have with it so far is that I no longer get notifications while I'm in my car (again, maybe unrelated to the Pie update). Otherwise it is behaving almost like a new phone again like it did back in October, or maybe even a little faster.