[...]Great name or site functionality or both?
Both!
The name of your website should be easy to remember so that whenever user want to gamble he/she will revisit to your website. And if the name of your website/domain name isn't easy to remember, then your users will forget your website name as soon as they log out from your website, and the next time he will go to that website which he/she remembers. Therefore, an easy-to-remember domain name is very important in my opinion.
The functionality is what makes you different from others.
I mean If you provide more features than your competitors, then you'll have the upper hand over your competitors and People will be impressed with your feature list and they would like to play again.
Yes, functionality is very important.
It's like a chocolate candy. The candy can have a beautiful and bright wrapper. It draws attention. A beautiful and bright wrapper encourages consumers to buy a kilogram of these sweets.
However, the wrapper is not the main thing. The main thing is the taste of this candy. If the candy is not tasty, then the consumer will no longer buy this candy.
We value things for their functionality. They must meet our needs.
The functionality of an online casino site will make players come back again and again (to gamble).