It is especially nice that the ability to turn a face-down creature face-up is a static ability and not an activated ability. You can flip Zoetic Cavern even in response to Sudden Death or Sudden Shock.
As much as I like this card, however, I'm not really sure how much it adds to a deck. In many decks, it is merely adequate in the early game. Most of the time, I would rather see sources of coloured mana. In the mid-late game, it is likewise mediocre. Aside from dodging some removal, it seems that there are better creatures that you could be playing. It does yield some card advantage in the same way that the Ravnica-block karoos give you the effective functionality of two lands in a single card. Unfortunately, I am not sure that either option is worthwhile. Three mana is too much to pay for a 2/2 creature. It might dodge a burn spell, but the creature is still gone, even though the card remains. As a land, you'd be better off with a basic. Overall, I think that I'd rather play with Llanowar Elves or Utopia Tree if I needed a mana-producing creature or a basic land if I wanted 'just a land.'
You might argue that it lets you play two lands on the same turn, but it costs you five mana to do so. I think you'd be better off playing with Teramorphic Expanse, which also thins your deck in the process.
Jorael raises a semivalid point that it makes other creatures with morph better by association. On the other hand, you could make the same argument for Foothill Guide. (Hint: I don't consider getting a colourless land all that much better than getting nothing at all.) Whenever you have multiple face-down creatures available, an opponent with a removal spell is taking a risk by targeting one of them.
