Atlantis Down is definitely a must see movie. It keeps the suspense very high from the beginning to the end of the story, making you continuously wonder what's coming next.
Oftentimes, it reminds of Hitchcock's movies when several possible shocks occur completely breaking the expectation based on the previous scenes.
At the end, still many interpretations are plausible. It's a never-ending story, or a story where it's up to the watcher to decide what the most plausible end of the movie should be among the several underlined by the developments.
It's intriguing and deep. It makes you think, and you do want to watch it again.