I liked it a lot. One of my favorite sub movies. I thought the crew acted very realistically. Not like the typical Hollywood submarine garbage. They were dirty, ugly, foul-mouthed... just like the real thing!
Also, anyone using TMO will recognize some of the dialogue.
I also liked...
*possible spoiler here, stop reading if you haven't seen it*
...that they never really confirmed that it was a ghost.... so that a really skeptical person could still believe that it was just a major coincidence spurred by a widespread psychological breakdown. Very cool.