I finally got through it and I thought it was an excellent book, tied together the big picture of the war at sea during WWI much better than anything else I have come across. It also gave a thorough and detailed but easily understandable description of the Battle Of Jutland. Most of the histories I have read of that were almost too detailed and focused on many of the individual actions while Castles of Steel focused on the bigger picture.
A couple of observations; Germany comes across as the bad guy again just like in Dreadnought (except for Bismarck they really don't seem to do 'big' strategy very well at all and they were really arrogant), Jellicoe comes across much better by far than Beatty even on a personal level, Churchill learned some hard lessons but I think he came out better for it when his country needed him 20 years later and command and control in in the thick of a naval battle is really hard (a lesson from Neptune's Inferno too).
If you have the time I highly recommend both Castles of Steel and Dreadnought, I read them in chronological sequence and they fit together well.
Do these books assume a decent knowledge of the events surrounding WWI ? Also, have you read Sleepwalkers or Guns of August?