I admit to be rather harsh in the overall rating of this otherwise great documentary. But his has to be said that the video is grainy throughout and the sound is just horrible by modern standards. A constant backround hissing sometimes underlayed with a deep tremor. Adding to the grainy images sometimes the lens is dust specled. Just by the fact that David is in full hair and not the least bit grey should say something about the date of the original film material. Still, you would need a high end TV and Sound system to be put off by it. The content is as allways, by Sir D. Attenborough standards, superb. But not easily digested like Earth or Blue planet. It delwes more into the chemical and biogenetical issues of the matter and requires time and concentration to be fully apppreciated. Ah, and one more point, it is 4:3. So that gives you quite a nice set of black bars, left and right on your 16:9 sized TV-set.
So, despite the great content, I still gave it "only" 3 stars to make a point. Because I would have liked to have known this beforehand.