As for me, the most important feature would be having a good help desk or customer service. This is because when problems and inconvenience happen, it'll be less of a hassle and a stress if you have a nice representative you can run to to ask solutions and troubleshooting advices. It will be great if the casino is willing to help and cooperate with you to solve your concerns. If a casino don't possess this feature, isn't accommodating and approachable, then expect to be disappointed and to encounter chain of chaos.
My top three from the list you've mentioned are as follows, in chronological order: the good help desk, strong community/reputation, and good looking/fast user interface. All of the other features can come in any order, I won't really mind but these are my top priorities if ever I will engage in gambling or if someone will ask me about what they should look for in a website.
We can agree that a good customer service is important, in case we run into troubles while trying to withdraw, for example.
But, I personally believe that the best case for a casino and their gamblers would be to have an intuitive enough interface and system, so clients won't easily find any troubles while gambling.
In short, if a casino need to have a big costumer service department (in comparison to the number of gamblers they carter), I would assume they need to invest more in their platform. Of course, that is just some random thought I just had while reading your post.