This review is actually pretty simple:
If you saw discs 1 & 2 and loved them, go ahead and get these.
If you saw discs 1 & 2 and were ambivalent, this won't change your mind.
If you didn't see discs 1 & 2, what are you doing here? Go see them!
With that out of the way... I liked these, but the "wow" factor of the imagery is nowhere near as high on these discs as on the first two discs. Parts of these episodes feel like re-cycles from prior discs (how many different scenes of whales and birds eating up shoals of fish packed into balls do we need?), and the long segments on seafarig birds felt out of place. Also, some really suspect computer graphics work rears its head in these two specials a bit too often, which really pulls the viewer out of the experience.
Still, that being said, these are darn good documentaries for eye-candy, and leagues ahead of the competition. It's just that compared to some of the jaw-dropping material on discs 1 and 2, these two come up somewhat lacking. I don't regret purchasing them, I just know that in the future I won't be re-watching them anywhere near as often as discs 1 and 2.