It's based on real life events, so I realize you can't really embellish it like an entirely fictional film. But you see some attempts at character-building, but in the end, no character really stands out or has any depth. Characters are just discarded--the wife (played by Elizabeth Shue for all of one scene and a flashback), the first officer, crew members, etc. It just becomes a series of naval combat action scenes. As many reviewers have commented, the movie feels like it's too short and missing something.
There is a hint of something there--the frustration, dread, and the conflicting emotions of having to make difficult decisions of protecting a large convoy with limited resources. But Hanks plays a captain who supposedly is an inexperienced commander on his first command, having to face the full onslaught of an experienced German Wolf Pack--the problem is, he is so calm, collected, precise and intuitively makes all decisions correctly, it's not believable. Again, it's entirely feasible that the real life captain was exactly that and this was an extraordinary accomplishment, but as a movie, he just comes across as any commander with exceptional anti-submarine warfare experience, with none of the vulnerability, fear and doubt. The "cat and mouse" hunter vs. hunted tension that one would come to expect from a movie involving sub combat feels somewhat lacking.
The action sequences are very good and seem realistic. But in the end, there's not a lot of substance, and you won't feel very emotionally invested in any of the characters, the way we've all felt watching movies like Saving Private Ryan, Das Boot, Fury, or any number of excellent WWII movies out there. It's certainly not a bad movie and enjoyable to watch, but understand that it's very limited in what it portrays.