I used it on a walk yesterday. It was a little clunkier than notification announcements but otherwise, I didn't hate it.
There are two voices right now. The one you heard in the keynote is Sam Sanchez.
The other is Jamie-Ray Hartshorne.
I think the reason I don't mind it is I've spent a lot of time using Apple Fitness+ and this is like that but mobile.
I'll keep using it.