This is probably the best textbook I've ever used. Last summer session, I took an online, university-level Oceanography class and this was the main text. Although some concepts in oceanography are difficult to grasp (usually due to the abstract thinking required to comprehend them) this text made everything as easy as possible. There are so many different ways the information is presented--written text, videos, graphs, charts, infographics, real world examples, etc.--there's definitely something for every learning style. I constantly found myself making use of the text's search feature, as well; it was invaluable.
I've had other e-texts before, but this is the first one I've used that really puts the digital platform to use in a way that is effective and easy-to-understand. Indeed, this is the first time I've felt that the digital version of a textbook must be better than the physical.