Well, if you're looking for a comprehensive book on the u-boat war in all theatres during WWII, this is it. If you're looking for a humongous doorstopper to hold up your desk, it'll serve that purpose too. I got about half way through before the detail threatened to make my head explode and I started to lose the thread of the overall campaign. I was also slightly disappointed because my history teacher used a quote from Clay Blair that implied he thought the u-boat war was never particularly dangerous, but although you do get the impression it could've been a lot worse, what happened seems bad enough to me.
An exhaustive (and exhausting to read) catalogue of every u-boat action, and every attempted u-boat action, along with great technical detail about the u-boats themselves and the convoy system and the commanders and... Yeh, you get the picture. I suspect it's the biggest book I've ever seen, except maybe the Bible (which, admittedly, I have read all the way through twice over now, including once in 90 days which was pretty fun), and this was only part one.
I don't think it was meant to be read all the way through. In fact, although it starts off feeling pretty readable, the sheer quantity of information and detail just makes it impossible to read right through. As a reference, I suspect it's incomparable, with a heck of a lot of detailed research work going in to work out exactly which sub sunk which ship and when torpedoes malfunctioned and which ship was doing weather reports when. So if you fancy having a reference to every u-boat operation during WWII, and a nice and to be fair rather interesting, chunk at the beginning about the development of the u-boat arm and the specifications of the ship, this is the book to get.
One other thing I will mention that struck me was the sheer number of times the German torpedoes malfunctioned. Although the Battle of the Atlantic initially went rather disastrously for Britain, the number of ships saved by the torpedoes failing to detonate, or because the magnetic torpedoes which would 'kill' a ship with one torpedo rather than the contact pistols which usually needed two or three torpedoes per ship were utterly useless is quite astounding. In the end, the Germans resorted to copying British torpedoes which kept depth far better. So we were better with them at some things...
An interesting book then, if you've got a lot of time to read it or if you want to use it as a reference.