I liked it. It's worth a watch.
It's no 'Das Boot' but anyone who is into submarine movies should definitely give this one a shot. It was filmed well. The tension onboard the sub keeps building more and more as it went on.
I think the acting was good. Jude Law was impressive in this in my opinion. But I think they did well choosing the cast, they seemed to be believable in their roles.
Special effects weren't too bad at all, I expected that aspect to be terrible.
I gave it a 7..
..as I was searching for used submarines online.