BBC nature documentaries are always entertaining and educational. They are also often spectacular. Hammerhead is comparatively, a lesser offering. Though it is informative, you get the feeling there is a bit of padding in this production. The hammerhead shark lives in sometimes murky waters so that also affects picture quality. The special feature on this DVD is the 2004 Natural World documentary Shark Coasts with David Attenborough
Hammerhead sets out to explain why the hammerhead shark is the way it is and why it is shaped the way it is. Both questions are answered and the answer to the why is fascinating. You learn about the mating habits, why the hammerhead especially likes Hawaii for birthing, the explanation for the great congregation of hammerheads that occurs once a year (a Montreal road construction traffic jam is peanuts compared to this), and a few other interesting facts.
One thing BBC nature shows are known for is for the beauty of the images. This is rather lacking here. If you are interesting in sharks Hammerhead is a good bet, if you are more interested in nature in general, there are lots of other BBC documentaries reviewed on this site that will satisfy more.