It is rare for a Saturday evening mainstream entertainment show to take on such topics as slavery and exploitation of an entire race. It isn't exactly something that keeps television executives awake at night, wondering how they can incorporate these issues in to their next production. However, this is what the latest episode of Doctor Who managed to do - while at the same time retaining all the essential ingredients of broad family entertainment. There were the usual elements we have grown to expect - chases, mysteries and lots of grisly deaths but with the addition of demanding questions around human morality at its core.

The episode starts in a wonderfully cheeky way, an advert expounding the virtues of the Ood as the ultimate servant. They even make your tea! Throw in a heavy dose of corporate greed and the audience knows full well that there is going to be a shock in store for us before the title sequence begins (and I love the new version of the theme by the way, nice and heavy on the bass!). Sure enough, this episode does not disappoint.
Planet Of The Ood reintroduces us to the species that we first met in the last series in The Impossible Planet and its sister episode The Satan Pit. If they were spooky then, they are down right frightening in this episode. The Doctor and Donna come across a dying Ood in the snowy wastes of its home planet. Before the creature expires, its eyes glow red which leads the Doctor to wonder if his enemy from the previous series has somehow residually survived through some form of telepathy.
At the same time the human controllers of the Ood Sphere are having trouble with “red eye” themselves, with some of their Ood even becoming apparently rabid. With the Doctor and Donna infiltrating the organization (didn't they do that in episode one?) the Ood finally have allies that they can trust. The Ood have previously been presented to us - and their human “owners” as simply a servant race, one which humanity stumbled upon and effectively rescued from a meaningless existence.

In this episode we come to realize - along with the Doctor who abandoned their fellows to a black hole - that there is much more to the Ood than meets the eye. They are a hive creature, effectively, who have two brains. Peaceful by nature, they are born with their second brain in their hands and use this to connect with the larger (much larger!) single brain that acts as a coordinator of their gift to the universe - their song. A gestalt like organism they are individually little use but when they come together they produce a song that is a combination of subliminal worship, wonder and innocence. Humanity has effectively lobotomized them by replacing their external brain with the translator device each is then forced to carry as a terrible and constant reminder of what they have lost.

This was a deft touch by the writer, Keith Temple. Most people are aware of whale song and this - plus the fact that we have hunted whales almost to existence - no doubt resonated with much of the audience. It is one of many visual nuances that this episode provides to ease the viewer through the lack of time the writer had to fully develop his ideas.
The Ood planet itself is beautifully realized but Donna initially doesn't seem terribly impressed because of the weather. However once she dons a warm coat she takes in her first alien world with relish - and even manages to get a sly dig in about the size of the Doctor's “box” at the same time. It is a relief that the Time Lord finally has a companion in the series who has a wardrobe that consists of more than three pieces of clothing and a mouth that borders on the blessedly cheeky. As we saw in Partners In Crime, Donna has brought her entire wardrobe - and ever so slightly bitchy wit with her and it pays off almost immediately. For sheer organization and for want of a better word, lip, she already outshines Martha and Rose!

Catherine Tate continues to surprise and delight. I am becoming accustomed to her odd foray in to her “show” characters and am beginning to think that she put more of herself in to them than previously met the eye. Would I be going too far to say that in Donna Noble, she is almost effectively playing herself? That would certainly explain the way that her character articulates when shocked, excited or just plain terrified! When the Doctor links her up telepathically so she can hear the captivity song of the Ood it was one of the more touching moments of the series so far. Tears were shed not for herself or her family but for an entire species. One could almost see the enormity of the truth realized on her face. She is unable bear their song for more than a short time so sorrowful it is in their bondage.
Another thing is that you have to pay attention to the chemistry between the two principal characters. There seems to be none between these two. There was a significant amount of chemistry between 'Rose' and the Doctor and a nice healthy amount between him and 'Martha'
Just a note, when you said that mankind has hunted the whales almost to.... did you mean extinction?