I have endless frustrations with Google Assistant / Google Now / Whatever they call it now. A few examples:
1. I have my phone set up to trust bluetooth in my car and unlock my phone. I get in the car and say "okay google, open spotify" -- this is so that it will continue playing what I was listening to before I left work.
"Okay", she says, and then tells me that she can't do that because my screen is locked. Sometimes this works, and sometimes it does not.
2. When I had Google Play Music it reliably would play random sub-par covers of songs rather than the original, even when I specified the artist.
3. Sometimes it decides to rely on screen input instead of audio controls. I can't do that while I'm driving.
4. It sometimes ends voice input too early or does voice input inconsistently. I've sent messages to my wife saying "I'm on my way home exclamation point" instead of "I'm on my way home!"
5. Commands which have worked for months suddenly stop working.
6. Sometimes my screen stays on, forever, after asking to play music. (OnePlus 7T, Android 10). This does not always happen.
7. Google: "Here's your message, send it?"
Me: Yes
Google: Sits there for a moment and pops up the results for "Yes" in the assistant.
My biggest gripe isn't what it can and can not do. It is the inconsistency that drives me up the wall. I am not a heavy user and most of my requests are because I wish for it to be hands-free in a car with bluetooth audio. I'm sure that this is a harder problem to solve than just me interacting with the phone, but it is a common use case.