You can check Rollbit and Stake, the sites have good UI/UX
Not clearly a UI/UX enthusiast when it comes to gambling platforms, I'm into more on the customer protection and the same stuff. I know we've been into these casino before that aren't that fancy but still we love to play on it, I guess the UI/UX are just the side dishes for me when it comes to playing in a casino.
Maybe you do not like in-play, I like UI when it comes to live matches. Also a gambling site that do not have a good UI may discourage people and move to the ones that provide good user experience, good interface is part of the good experience customers will see if using a gambling site or any other sites. There are gambling sites that are providing excellent UI/UX and very reputable, having the characteristics that can attract new users.