I have noticed that the caves are very rare and empty. People mostly just get the resources from the top of the planet and don't even bother to do some caving. If you add traps, more mobs, more loot and ores caving would become a very fun thing. There just isnt enough action or reward !
Uh. You do know there's no ore (except for coal) ontop, right? You practically have to dig downwards if you want to progress in the game. (^ Unstable/Nightly)