Nice take to the challenge. The main probably here is the contrast. It fine on the foreground but with the rocks in the back and the water it just looks flat. Not anything you can fix in basic editing really so I probably would have tried to minimize that problem when composing this (i.e. more beach in the shot or have the dogs closer to the water if possible).
What fun! I wish there were fewer dog butts (sorry) in the shot and we got to see more of their faces. But I really like the two dogs in the surf - the illustration of so many dogs enjoying themselves in different ways really makes the photo. 7