Voice input is a terrible UX, because as a user, you have no idea what the system can and can't do. Every single Voice UX I've used for input (Siri, Alexa, etc) is a fumbling around experience where inevitably I can find out the weather, turn on some music, and then hear some half-funny replies from the device because it doesn't actually know what to do. It can work 99% of the time, but if that 1% it breaks down and I have to revert to a device with a screen, it kind of ruins the point.
Maybe Amazon is addressing this with their supposed Alexa with a 7" screen in the future.
What I want is improved Voice Output UX. I think Apple is trending towards this with the AirPods, where you can leave them in your ears all day and have Siri just talking to you, which is the only practical use of any of these things unless you're stoked about annoying everyone around you with your robot assistant awkwardly talking out loud all day.