They were not given enough personality to distinguish them apart, something that is essential for us to care about their fate. Submarines and costumes looked worn and genuine. The photography was remarkably claustrophobic in the submarines. External shots appeared to be of authentic submarines not miniatures or computer generated. As good as the movie is, you've seen every situation in other submarine movies.
Subs going too deep, hatches blowing and a lot of water filling the subs are standard stuff.
U-571 does take a short break to portray the Germans as more than just evil drones. When a German U-boat encounter a group of refuges on a life boat a reluctant gunman is told that he has to kill them. The German Captain coldly explains that if they are allowed to live the refugees will give away their position and Hitler has issued a no prisoners order. Maybe, but the movie would have been far more interesting with more scenes like that and less of the endless action. U-571 is excellent entertainment, but it's not an original entry into the submarine war movies genre.