The original Open Water had a couple stranded in the high seas when they went deep sea diving, and somehow missed the boat, literally, thereby being stranded in the middle of nowhere. The formula is now repeated in Open Water 2: Adrift (just called Adrift here probably to disassociate itself from being a "sequel of sorts" movie), with the number of couples increased threefold.
But I can't judge which is better, having not watched the original. Adrift though seemed decent enough, with human nature for self-preservation portrayed so starkly on screen, it's scary. And having to bump up the number of those in trouble, allows for different views and types of people (read: caricatures at times) to be showcased. Each cast member have certain strengths, and some just have total negativity built into them, for contrast purposes.
The setup is simple and we waste no time in being introduced to our characters, almost all of whom are high school friends, and gathered together to celebrate one of their 30th birthday. They go on a weekend cruise on a luxurious yacht, and it's party, party, party, enjoying the finer things in life. Until they decide to go swimming in the sea, did they realize that hey, did someone lower the ladder on board? Otherwise, how are they going to get back to the deck? It's down to the adage of looking before you leap, and that danger lurks when you're enjoying yourself so much, that common sense, precautions and safety get thrown in the wind.
And when the severity of the problem surfaces, what do you do? Are you the leader, the thinker, the whiner or the quitter? When everything is fine and dandy, everyone knows how to enjoy to the max. But when there's an issue at hand, do you begin to point your finger at everyone else, or help to think of a solution? And when all seems lost, do you give up, or try, try again? The characters partake in exhibiting some of these traits at different points, and with time running out, and dehydration, paranoia and hysteria slowing creeping in, you'd wonder how long they'll last.
It's human nature to instinctively try and survive, and watching the characters on screen do just that in spite of impossible odds, just makes your heart pound faster as you think - what would you do if you're caught in the same situation? Would you bitch slap the complainer? Would you follow instructions to a T? Would you give ideas and shut up when it doesn't work? And when all seems lost, what would you do?
Supposedly based on true events, this story might have its plot holes at certain times when you think, hey they should have done this or that, but I'd suggest to hold onto your train of thoughts, until a key revelation is made, to which you may nod in agreement why it happened the way it did, and that shake in disbelief when you think that when it comes to life and death, material things should be sacrificed first, and facing the music is just part of the inevitable consequence.