As a submarine movie, it is great. Unlike other movies, it is very realistic, showing the claustrophobic quarters and the close contact of crew in a submarine very well.
One issue I had with the movie is that it seemed a bit longer than it should have been. I looked at my watch a few times while watching it. I guess I would have been better off watching the theatrical version (2.5 hours) instead of the Director’s cut (3.5 hours) that I watched.
Oh and I really liked the ending.
I would rate Das Boot 8/10.