I'm facing the same issue.

What do you mean by terrible? As in, it doesn’t respond or pick you up or is the response incorrect?

I also have this problem.

We had a good quality Bluetooth speaker which we never used since we got a Google home mini. Even though the sound quality was rubbish, the assistant was a game changer. We then bought into sonos to merge the best of both worlds.

Even though the sound is superb, the assistant is awful. The Google mini just worked, every song request or volume adjustment worked instantly. The assistant on the sonos is so frustrating and hardly ever works, especially not first time. Half tempted to send them back on this basis. 

I waited a while for the Sonos One to have google functionality since I also found the google experience via a google mini very impressive and so easy to use but wanted the improved sound quality. Unfortunately, I have been trying to get two sonos ones to work with google for nearly six months.

I have had enough now so called to return them as faulty earlier today.  It is ridiculous all the solutions/work arounds that everyone is having to invent/come up with to try to get it to work with Google Assistant. You shouldn’t need to do this. It should just work! What are Sonos doing about it?! It seems they are doing very little to me or if they are working on it, they are not having much success. 

Similar to Liam, I just wanted it to work in the same way as the google mini but with improved sound quality but the google aspect hardly ever works. Without this it just becomes a bluetooth speaker which I already have. I am going to try something else but not quite sure what yet! Sonos with Google Assistant clearly isn't an option at the current time. Any suggestions are welcome!