If only they kept it more realistic
It could have been a better movie.
What bugged me:
Blake Lively has perfect vision underwater and she could see the jellyfish from the surface while the water was very agitated. Also once she is swimming among the jellyfishs, it's as if the water was perfectly still. Currents are not just on the surface of the water. The jellyfish should have been shifting left and right.
The shark had a whole fat whale just for himself and somehow he bothered going after tiny, bony humans.
They way she killed the shark...I doubt the weight of the chain would have been heavy enough to drag her down faster than the shark, and again, how did she see the spikes on the buoy's anchor so perfectly?