I used to worry about the way there was no limit to the number of times a character could use a move like Shapeshift or Cure Light Wounds or Fireball. But the better I get at GMing this game, the less of a problem it is, because I've learned how to make my players afraid of the failure. With a +3, maybe they'll only fail one time in 10 or so, but oh, how badly I can make them regret a fumble at the wrong time.
It's a magical transformation of your entire body – *anything* could go wrong. Get stuck in animal form with no hold for moves. Shatter some gear and get stuck with it wrapped around you. Get wracked by pain and end up temporarily helpless on the ground. Get the wrong form entirely (hello mouse). Get the form *too* well, so you're overcome by animal urges and forget your human goals. Get a geas from the Powers of Nature to do what *they* need.
As DM, find the result that makes them groan, "oh no, of *course* that would happen!" If it fits in the fiction and doesn't take anyone too far out of the game, anything is fair game. They picked up the dice, so they knew it could happen.
You want players to think twice any time they pick up the dice. It's the key to making this game shine, and IMHO, the biggest reason you would choose to play it over regular D&D. Whatever you're doing, it can *always* go wrong.
(You've probably also found by now that the Druid is far from the only character with a powerful move that can mow down mooks. Not many ordinary goblins are walking away from contact with the Fighter or the Barbarian either.)