This series has a lot going for it with beautiful footage of the some of the most impressive underwater environments on this planet. Being a staggering five years in the making, one would be hard-pressed to expect any less. I did get the impression that some scenes from the first episode where repeated in the latter ones, which is naturally only a minor gripe.
David Attenborough is great as a narrator and comments are informative, leaving enough room for one's imagination, and well spaced out, so that viewers get plenty of time to reflect upon the breathtaking imagery. If you get the opportunity try not to watch a translated version of this series.
A definite must-see for anyone interested in the intricacies of our blue continents and easily the best documentary on this subject I've ever seen.