You have a good start here and I like that you have a reference image. You have good overall rendering and good size variation in your brick pattern. You even have the start to a little height variation. It tiles nicely when I tested that too.To take it further, I'd like you to push and pull some of the bricks a little bit more and add a little more color variation. You can see that the reference image you used also has some of the recessed and raised rocks that you have, but they are a little darker and a cooler, grayer color when recessed and brighter, warmer colors when popped up. By adding the cooler/warmer colors to the pattern you'll hit 2 birds with one stone: a touch more height variation as well as color variation.