I just checked. Unless I'm missing something there is no simple volume control like on the physical keyboard? I already have the volume button on my touchbar home screen however tapping it opens a slider. I don't want or need a slider and have to do a tap and then slide to get the volume down whilst before it was one press of a button. This usually requires me to look away form what I'm doing. It's definitely a step back in terms of UX. It was perfect before the touchbar.

Thanks for pointing that feature out though. Have replaced Siri with the play button :)

Edit: Just playing around with this a bit more I noticed the expanded view now has all the normal icons. Either I missed it before or I changed something. Is there a way to make the expanded view the default?

You can tap-hold-slide to adjust across the whole range, rather than tapping then hunting for the slider. You can also set the touch bar to show an expanded control strip by default (which includes a volume up/volume down/mute triple) if you want.

The tap and hold works well. I guess I will settle on expanded view with fn key for app controls. Probably the best for my usecase.

I have the problem where the TouchBar goes blank and it's not even detected by the system any longer (System Preferences - Keyboard) and I have to reboot to get the controls back.