Icy Moons
If any planetary moons should be alike and equally dull it would be the regular moons of Saturn and Uranus, but even then they're as alike as they are different. Compare Mimas and Miranda, for example, or Rhea and Titania. They all show extensive cratering (which no one expected) and signs of geophysical activity (which no one expected either), and yet they all have a different style of each.