I don't need to repeat again how good this series is so I'll just say that if you think there's even a remote chance you'll enjoy this then you should watch it.
Some reviewers have complained that it's 60i. Extras aside, it's not. The main series is 24p (60i with pulldown). The picture quality is also great with only occasional non-HD parts. Night scenes are obviously going to be lower quality. It's not like you can set up a lot of spotlights just to get a nice picture.
The downside? Unfortunately the BBC have decided to compromise this version, presumably for the US market. The episodes are indeed 24p. However they should be played back at 25fps, not 24. In other words it's too slow. The audio also suffers because of this. It's been slowed down and pitch corrected. This leads to some unpleasant artefacts that are easily heard during the orchestral score.
The Snow Leopards / Desert Lions extras suffer too. Again both should be 25p. One has been interlaced to 60i, the other blended to 30p. At least the audio's ok on these.
So I'm torn. On one hand it's still a fantastic series. On the other I don't want to encourage these kind of authoring issues.
In the end though the quality still shines through, so I'll just drop a star because of the problems.