My thoughts:
It is much too small. Look at the size of a physical key compared to the Touch Bar. Such a pain to use.
It is in the wrong place. It is so awkward to be constantly reaching over the keyboard to use these buttons.
Touch means that you have to be constantly looking down. This goes directly against a large pat of the functionality of using a laptop or desktop; the advantage of only needing to look at the screen is dashed by the Touch Bar.
It seems that this misguided Touch Bar is an apt metaphor for the mess that Apple is in at the moment. Apple used to represent focus under Steve Jobs. Laser-sharp focus. That was his mantra. Yet with this Touch Bar, one is constantly losing focus by glancing down at the keyboard then glancing up at the screen. That seems to represent the lack of focus that typifies Apple under Tim Cook.
One or two others have mentioned this: I think that if they wanted to introduce additional touch functionality, they should have used the existing trackpad and created some icons around or in it. There is a large amount of space around the trackpad, and it is more natural to use that space for touch. That, to my mind, would have represented an organic development of the trackpad, and been a better application of touch.