Beware: spoilers for everything from 1x13: The Parting of the Ways to the 2nd Christmas special and series 3!
Okay, first of all: Rose. We know this is her last episode. The big question is, does she die or does she choose to leave the Doctor? I know the voiceover says she dies, but... the shots of her on the beach alone? To me, that is a Rose who's left the Doctor. There's a maturity and a sadness there I don't think could have come from anything else.
Naturally I don't want her to die, but I can't see any reason why she would leave the Doctor. So perhaps she will be like Jack and die before being brought back to life somehow. And either the Doctor will have already left, as with Jack, or that will make her choose to leave.
Also, the trailer shows that Pete is in it. Yay! Am I the only person thinking, "they've killed off Earth!Pete and alternateEarth!Jackie ... now the Pete and Jackie left can hook up"? XD; No, I don't think it would be an OMG-my-true-love-has-returned thing, but a kind of angsty, you're-so-similar-to-my-dead-spouse thing.
And I wouldn't be upset if Rose got back with Mickey. Mickey's cool now. Mickey's got guts. He is a Mickey that could match Rose. He's a Mickey worthy of Rose. Yes, Doctor/Rose is adorable - but he's immortal, she's not, we all knew it was vaguely doomed.
So... after Rose, the new companion.
Ever since I heard Billie Piper was leaving, I began to think, "who could play the new companion?" And every time I saw a new character in the series, I was assessing them for the companionability.
When Adeola came on, I was thought, "hey, she's cute, maybe she could be the new companion!" But then she died, and I was sad. But the same actress has been cast as an entirely different character (with different last names too, I've discovered, so presumably not related) so hurrah! I've heard some people saying that she didn't do a good job with Adeola but I thought she did. Also, people are complaining about her having two different parts so close together... Well, not really. She's not in the Christmas special. So it'll be April-ish before we see her.
...Yeah, okay, so we'll still know it's the same actress. But give her a different hairstyle, different clothes, different make-up, and - if she actually is a good actress - a different air, and I think it'll be obvious it's not the same character.
Talking of the Christmas special... Torchwood will have aired by then. Who wants to bet the "surprise" will be Captain Jack?! XD; (Well. Maybe not. But it would be cool!)