As a demo at least, this doesn’t look bad at all. I think it really drives home how voice-driven devices like these need to be, which is where some of this falls down for me.
If Siri were the only (or at least main) control scheme for my watch, there’d be lots of times I would’t be able to fully use it. I work in an open office, and would never use Siri at my desk. Likewise, I often look at my watch while watching a movie, at church, while with a resting child and in about a billion other situations where silence is critical.