Being a huge fan of the Das Boot book, film and original TV series in 85, I'm very impressed with this series.
I've read other comments from other critics here and I'm surprised that there are some who are comparing this show with historical fact?
I don't think they actually understand that the original book/film is based on multiple true U-boat stories but its not a documentary, its still considered fictional and for that matter, Lothar Gunther Buchheim, (author and consultant on the Das Boot film) didn't really like the film. My understanding is he gave Wolfgang Peterson a hard time, was difficult to work with and was disappointed.
So, if you read Deveton's post, I would disregard it. This person stresses how conveys went so many knots, the style of the ships, or the depiction of certain battle scenes and how it's all inaccurate. I'm surprised I didn't read how the show didn't use original German cigarettes, that the color of the uniforms were wrong or that a picture in a background scene hanging on the wall was crooked. Lighten up Dev, it's a show! By the way, ships in WW2 did have diesel engines.
Anyway, beyond what others say, if you're a fan of the Das Boot film/book, I think you'll enjoy the Series even if its not a Documentary.