Castaway meets Open Water, Baywatch, and/or Farrah Fawcett.
I'm always sorta amazed by movies that are so simple and elemental: woman, rock, dorsal fin.
The Shallows is beautifully filmed, the bay of Lord Howe Island (Queensland, Australia) stunningly gorgeous. Blue sugar.
It probably warrants only a 7, but is somehow very gratifying nonetheless.
If you suffer from galeophobia or vasovagal syncopy, however, you are chum, sista.
