I had a crash or two in my first month, but it escalated on Nov 22nd when I had four crashes in about an hour. I was trying to ride up Alpe with workout set. I would barely finish the warm up (once I did not get that far), and then Zwift would just disappear and I would be left staring at my desktop 
I checked this forum and used some tips (change the resolution, switch to windowed mode, check log file against zwiftalizer, kill unnecessary background apps etc.) but I ended up with four rides 6-20 minutes long. I gave up, checked support page and opened a ticket submitting relevant information about my setup and logs according to instructions from support pages (forum does not let me include links)
Next day (Nov 23rd), I’ve got an email that my ticket was escalated.
On Dec 8th, somebody asked me to send a Zwift generated file with my computer specs, so I did.
On Dec 22nd, I’ve got an email suggesting to update graphics driver. If that does not help, they can investigate further if I provide log files - the same ones which I had provided one month earlier when opening the ticket!
So, after a month, I did not move an inch. I am not paying to be getting frustrated when doing my indoor training, my wife does it for free 
I cancelled my subscription and may try again when this product gets more mature and starts appreciating it’s customers, not just trying to ■■■■■■ money and pretend all is good.
I work in IT, I provide support for some customers and I also use support from various vendors. I can recognize a support crew trying to fix something and support which is there to buy some time until problem goes away by itself (or customer gives up). Unfortunately, Zwift support is prime example of the latter. And to be clear, I received emails from three different persons, it is not just one bad agent.
So, there is my feedback: program is buggy and support is way too slow and useless. They did not give me any information I did not already find/try by myself using support pages or this forum. They did not give me any instructions or helpful tips which I did not try even before opening the ticket. They did not give impression they are trying to find out what is wrong. And most importantly, they did not find the cause for crashes and did not fix the issue.