The image shows the shadow of the rover, securely positioned on the surface of the red planet. It seems like a boring image, but it's extremely important. It means that everything is OK, that the rover is on firm ground and ready to start moving when Mission Control gives the order. It's also the pinnacle of the landing, perhaps the most amazing achievement in planetary exploration after the Apollo missions.
More images are expected in coming days. The first horizon image should be coming any time now. The first high definition panorama, however, is a week away. Both should be amazing, showing a gigantic mountain: Aeolis Mons, commonly known as Mount Sharp.
Update: Here's the third image. The dust has cleared and you can see what could be the rim of the Gale crater in the horizon.