I've made a couple of changes that have started to make the game feel a bit more like what I intend.
For one, I've reduced the HP of the player by two thirds. This has revived the dangerous feeling of the caverns a bit after I've taken the teeth out of just about everything down there in search of my goal.
Secondly, I've modified some of the animal behavior in very simple ways. Predators will now take attacks of opportunity against prey creatures, though they won't hunt them yet. Prey creatures will try to stay away from the player, though unfortunately they still retain the need to hunt the player, so they're eternally torn in a foolish dance that eventually just gets them killed.
I've got a long way to go...