This is a great book for anyone with an interest in underwater exploration. Hamilton-Paterson writes without a lot of the technical stuff that this sort of book tends to get bogged down in and tells a good story of a great adventure. His style is easy to read and at its high points impossible to put down. It's the best thing I've come across so far for telling you what it's like to be on these expeditions where the target is sunken treasure and he captures the highs and the lows brilliantly.
That said, don't expect Indianna Jones at sea. Three Miles Down is a serious account of a serious undertaking and an excellent piece of journalism. A definite good buy.