This really was an interesting episode, though. It's full of wit and drama and all that fun stuff...as well as more mystery. Let's take a look, shall we?
Wow. If that's not a pretty picture, then I don't know what is. But what is this picture, exactly? Well, it's the year 5.5 /apple/26 of course! Five billion years into the future. The day the SUN EXPANDS. Basically, Rose and the Doctor are crashing a party on the famous satellite 5 (gotta love that slightly psychic paper). It's a party where the best of the best and the richest of the rich come to watch this ancient planet roast. Now I'm not sure about you, but if I were searching for a companion, I probably wouldn't use the death of her world as a persuasion tool, but somehow it works for the Doctor and Rose.

Now when I say the "best of the best", I don't mean humans. In fact, Rose is the only human there... Unless you count Cassandra, of course, but who would count her?

Cassandra doesn't stop there, though. It's a bit subtle, but you may have noticed that she doesn't exactly look human. Sure, she has the fleshy skin-color and a brain (even if it is in a jar), but where is the flesh? This is the product of yet another act of brilliance on the part of the writer(s). Cassandra is the result of a thousand (or, rather, two-thousand) years of a ridiculously extreme desire to be thin. The first thing she says when she enters the room is a reference to the difference made in her figure from having her chin removed. Is this a statement about society or just British humor? Probably British humor.
...
Then again, when does this show not have to do with some sort of evil human quality?
After all, it turns out that Cassandra is more than just a flab of skin. She's an evil, greedy, murderous flab of skin. That's right, she's the villain in this plot. Her plan is to kill everyone on the satellite to make money. This, naturally, is proof that she is, in fact, human.
Not to worry, though, because there are living, humanoid "trees" around to help the Doctor save the world. Or...at least the aliens on board. The Earth still gets roasted.
That's all I have for this episode, though.
Stay moisturized!