I like what Deno is doing, it also has a bunch of great features. The functionality of it is great and the execution is sharp.
However, my main gripe with Deno is that it's tied to one company and it won't solve issues that it doesn't have. As an example of this, a version of nodes cluster module is not supported so there is no way of running one deno process per cpu which is very bad if you're hosting it yourself and want to utilize the full potential of your hardware.
It also means that if your app is bound to some CPU heavy action, like generating a large excel-file or similar, your app will go down since no requests will be processed due to the single thread nature. Of course, such actions can be solved with a web worker but what if you make a coding mistake which renders an unhandled exception? In this case the app would probably go down and if the end user for example does the same action over and over again (which end users tend to do in frustration), the app will go down again and again.
Deno as a company has probably little interest in solving this as the solution is to run it on their paid service. You could of course have several servers hosting the app, but that gets expensive real quick especially if you are a small shop. Another example is to run the entire app process as web workers but then you need to spin up many processes that all have their own ports which you need to add a load balancer in front of it. This is kind of advanced and adds unnecessary complexity to the app IMO.
Also, if Deno the company company fails, what then will happen to Deno the project?